[APM] Run APM e2e test uncondtionally

[sorenlouv]

In #113618 we had to disable APM's e2e test because they had started to fail. The cause was an update of hapi was upgraded to 20.2.0 which included a bug.
In #114414 hapi will be upgraded again with a patch that should fix APM's e2e's.

To avoid getting in this situation again we should run the e2e's unconditionally - and not only when APM code is changed.

This can be done by removing the whenChanged check:

kibana/vars/tasks.groovy

Lines 149 to 155 in 8a80c85

	whenChanged([
	'x-pack/plugins/apm/',
	]) {
	if (githubPr.isPr()) {
	task(kibanaPipeline.functionalTestProcess('xpack-APMCypress', './test/scripts/jenkins_apm_cypress.sh'))
	}
	}

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[smith]

APM E2E was disabled again in #114544.

[smith]

The latest failures don't seem to be from the issue with Hapi from before, but a failure on the error count test. Looking into this.

[smith]

This also fails intermittently: #109205. Will try to fix in the PR to fix this issue.

[smith]

I'm re-enabling them but not running them unconditionally. @spalger wrote a comment on the PR:

Sorry, but we don't run cypress tests on all PRs. That's the trade off of using cypress.

In a follow-up conversation in Slack:

Yeah, that's the deal that was made when cypress was chosen to begin with
Cypress is not supported, it's not recommended, it's not encouraged, and every chance we get to ask teams to use the tools we do support we take

Since running Cypress tests unconditionally is not supported, we are still open to the failure this issue was created to address, so our options are either:

• Use the stock FTR tools (selenium/webdriver/mocha/FTR) and rewrite all of our tests
• Continue to use Cypress and understand that if changes are made that break Cypress we won't be aware of them until somebody makes a PR that changes APM files

For now we're continuing to use Cypress and are aware of the risk. Closing this issue.