…astic#100056)

## Summary
fixes elastic#99895

Can reproduce elastic#99895 with something like
```shell
curl 'http://localhost:5601/api/fleet/enrollment-api-keys' \
  -H 'content-type: application/json' \
  -H 'kbn-version: 8.0.0' \
  -u elastic:changeme \
  --data-raw '{"name":"with spaces","policy_id":"d6a93200-b1bd-11eb-90ac-052b474d74cd"}'
```

Kibana logs this stack trace

```
server    log   [10:57:07.863] [error][fleet][plugins] KQLSyntaxError: Expected AND, OR, end of input but "\" found.
policy_id:"d6a93200-b1bd-11eb-90ac-052b474d74cd" AND name:with\ spaces*
--------------------------------------------------------------^
    at Object.fromKueryExpression (/Users/jfsiii/work/kibana/src/plugins/data/common/es_query/kuery/ast/ast.ts:52:13)
    at listEnrollmentApiKeys (/Users/jfsiii/work/kibana/x-pack/plugins/fleet/server/services/api_keys/enrollment_api_key.ts:37:69)
    at Object.generateEnrollmentAPIKey (/Users/jfsiii/work/kibana/x-pack/plugins/fleet/server/services/api_keys/enrollment_api_key.ts:160:31)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at postEnrollmentApiKeyHandler (/Users/jfsiii/work/kibana/x-pack/plugins/fleet/server/routes/enrollment_api_key/handler.ts:53:20)
    at Router.handle (/Users/jfsiii/work/kibana/src/core/server/http/router/router.ts:273:30)
    at handler (/Users/jfsiii/work/kibana/src/core/server/http/router/router.ts:228:11)
    at exports.Manager.execute (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/toolkit.js:60:28)
    at Object.internals.handler (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/handler.js:46:20)
    at exports.execute (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/handler.js:31:20)
    at Request._lifecycle (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/request.js:370:32)
    at Request._execute (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/request.js:279:9) {
  shortMessage: 'Expected AND, OR, end of input but "\\" found.'
```

the `kuery` value which causes the `KQLSyntaxError` is
```
policy_id:\"d6a93200-b1bd-11eb-90ac-052b474d74cd\" AND name:with\\ spaces*
``` 

a value without spaces, e.g. `no_spaces` 

```
policy_id:\"d6a93200-b1bd-11eb-90ac-052b474d74cd\" AND name:no_spaces*
```

is converted to this query object

```
{
  "bool": {
    "filter": [
      {
        "bool": {
          "should": [
            {
              "match_phrase": {
                "policy_id": "d6a93200-b1bd-11eb-90ac-052b474d74cd"
              }
            }
          ],
          "minimum_should_match": 1
        }
      },
      {
        "bool": {
          "should": [
            {
              "query_string": {
                "fields": [
                  "name"
                ],
                "query": "no_spaces*"
              }
            }
          ],
          "minimum_should_match": 1
        }
      }
    ]
  }
```

I tried some other approaches for handling the spaces based on what I saw in the docs like `name:"\"with spaces\"` and `name:(with spaces)*`but they all failed as well, like

```
KQLSyntaxError: Expected AND, OR, end of input but "*" found.
policy_id:"d6a93200-b1bd-11eb-90ac-052b474d74cd" AND name:(with spaces)*
-----------------------------------------------------------------------^
    at Object.fromKueryExpression (/Users/jfsiii/work/kibana/src/plugins/data/common/es_query/kuery/ast/ast.ts:52:13)
    at listEnrollmentApiKeys (/Users/jfsiii/work/kibana/x-pack/plugins/fleet/server/services/api_keys/enrollment_api_key.ts:37:69)
    at Object.generateEnrollmentAPIKey (/Users/jfsiii/work/kibana/x-pack/plugins/fleet/server/services/api_keys/enrollment_api_key.ts:166:31)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at postEnrollmentApiKeyHandler (/Users/jfsiii/work/kibana/x-pack/plugins/fleet/server/routes/enrollment_api_key/handler.ts:53:20)
    at Router.handle (/Users/jfsiii/work/kibana/src/core/server/http/router/router.ts:273:30)
    at handler (/Users/jfsiii/work/kibana/src/core/server/http/router/router.ts:228:11)
    at exports.Manager.execute (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/toolkit.js:60:28)
    at Object.internals.handler (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/handler.js:46:20)
    at exports.execute (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/handler.js:31:20)
    at Request._lifecycle (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/request.js:370:32)
    at Request._execute (/Users/jfsiii/work/kibana/node_modules/@hapi/hapi/lib/request.js:279:9) {
  shortMessage: 'Expected AND, OR, end of input but "*" found.'
```

So I logged out the query object for a successful request, and put that in a function

```
{
  "query": {
    "bool": {
      "filter": [
        {
          "bool": {
            "should": [
              {
                "match_phrase": {
                  "policy_id": "d6a93200-b1bd-11eb-90ac-052b474d74cd"
                }
              }
            ],
            "minimum_should_match": 1
          }
        },
        {
          "bool": {
            "should": [
              {
                "query_string": {
                  "fields": [
                    "name"
                  ],
                  "query": "(with spaces) *"
                }
              }
            ],
            "minimum_should_match": 1
          }
        }
      ]
    }
  }
}
```


### Checklist
- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios