## Summary

This PR updates FTR services to support authentication with custom
native role. Few notes:
- for compatibility with MKI we reserve **"customRole"** as a custom
role name used in tests
- test user is **automatically assigned** to this role, but before login
in browser/ generating cookie header or API key in each test suite
**role privileges must me updated according test scenario**

How to test:
I added a new test file for Search project:
`x-pack/test_serverless/functional/test_suites/search/custom_role_access.ts`

It can be run locally with:
```
 node scripts/functional_tests --config=x-pack/test_serverless/functional/test_suites/search/config.ts --grep "With custom role"
```

FTR UI test example:

```ts
// First set privileges for custom role
await samlAuth.setCustomRole({
        elasticsearch: {
          indices: [{ names: ['logstash-*'], privileges: ['read', 'view_index_metadata'] }],
        },
        kibana: [
          {
            feature: {
              discover: ['read'],
            },
            spaces: ['*'],
          },
        ],
      });
    });

// Then you can login in browser as a user with newly defined privileges
await pageObjects.svlCommonPage.loginWithCustomRole();
```

FTR api_integration test example:

```ts
// First set privileges for custom role
await samlAuth.setCustomRole({
        elasticsearch: {
          indices: [{ names: ['logstash-*'], privileges: ['read', 'view_index_metadata'] }],
        },
        kibana: [
          {
            feature: {
              discover: ['read'],
            },
            spaces: ['*'],
          },
        ],
      });
    });
// Then you can generate an API key with newly defined privileges
const roleAuthc = await samlAuth.createM2mApiKeyWithRoleScope('customRole');
// Don't forget to invalidate the API key in the end
await samlAuth.invalidateM2mApiKeyWithRoleScope(roleAuthc);
```

(cherry picked from commit f00ac7a)

# Conflicts:
#	packages/kbn-ftr-common-functional-services/services/saml_auth/serverless/auth_provider.ts
#	packages/kbn-ftr-common-functional-services/services/saml_auth/stateful/auth_provider.ts
#	x-pack/test_serverless/api_integration/test_suites/common/platform_security/authorization.ts
#	x-pack/test_serverless/functional/config.base.ts