… / Reporting (elastic#42804)

This PR contains enhancements to the `Cypress` end-to-end (e2e) testing support in the SIEM app, as discussed with @spalger

Note: this PR depends on test refactorings in elastic#42766

Cypress tests may now be run against a remote Elastic Cloud instance
(override `baseUrl`), interactively or via the command line.

Credentials are specified via `kibna.dev.yml` or environment variables.

Run tests on the command line (override `baseUrl` and pass credentials via
the `CYPRESS_ELASTICSEARCH_USERNAME` and `CYPRESS_ELASTICSEARCH_PASSWORD`
environment variables), via command line.

Reports are configured to include:

- An HTML report, suitable for e-mail notifications
- Screenshots
- Junit reports (for integration with Kibana CI)
- Videos (optional)

Reports generated when `Cypress` tests are run on the command line are output
to the `target` directory, which follows specific conventions used by the
Kibana CI process:

* Any directory under `target` that begins with `kibana-`, e.g. `kibana-siem` will be uploaded as an artifact to a bucket
* Junit reports are picked up from the `target/junit` directory

The artifacts generated by running `Cypress` tests on the command line conform to the above conventions.

An HTML report (e.g. for email notifications) is output to:

```
target/kibana-siem/cypress/results/output.html
```

Screenshots of failed tests are output to:

```
target/kibana-siem/cypress/screenshots
```

The Kibana CI process reports `junit` test results from the `target/junit` directory.

Cypress `junit` reports are generated in `target/kibana-siem/cypress/results`
and copied to the `target/junit` directory.

Videos are disabled by default, but can optionally be enabled by setting the
`CYPRESS_video=true` environment variable:

```
CYPRESS_video=true yarn cypress:run
```

Videos are (optionally) output to:

```
target/kibana-siem/cypress/videos
```

The full details and instructions for running Cypress tests are in the
`siem/cypress/README.md`, which was updated to reflect the changes
in this in this PR, but in a nutshell, you may run tests interactively with
the following (new) environment variables:

```sh
cd x-pack/legacy/plugins/siem
CYPRESS_baseUrl=http://localhost:5601 CYPRESS_ELASTICSEARCH_USERNAME=elastic CYPRESS_ELASTICSEARCH_PASSWORD=<password> yarn cypress:open
```

Running the command line version of the tests, which will output
the reports described above, is a similar experence:

```sh
cd x-pack/legacy/plugins/siem
CYPRESS_baseUrl=http://localhost:5601 CYPRESS_ELASTICSEARCH_USERNAME=elastic CYPRESS_ELASTICSEARCH_PASSWORD=<password> yarn cypress:run
```

elastic/siem-team#435
elastic/siem-team#437

- regen yarn.lock