functionaltests: Migrate existing smoke tests to functional tests

[ericywl]

Context

Smoke tests (especially smoke-test-ess) is hard to read and maintain, due to it being written in Bash scripts. It also doesn't support some additional setup / features that we will need to test more complex scenarios. As a result, we created functionaltests written in Go to eventually replace these smoke tests. However, current functional tests lacks a lot of the scenarios in smoke tests.

Testing Scenarios

TBA: scenarios will be taken from #15844.

Note: This issue only tracks scenario-parity of functional tests against smoke tests. Any new scenarios that we introduce in functional tests are discussed here.

Differences between smoketest and functionaltests

Feature	smoketest	functionaltests
Language	Bash-based (hard to debug sometimes)	Go-based (comes with all the Go testing goodness)
Test Versions	Mostly released / BC versions	SNAPSHOT and BC versions
Test Events	Only sends one event to APM	Uses telemetrygen to send a bunch of events to APM
Asserts Index & Data stream lifecycle policy	❌	✅
Asserts APM error logs in ES	❌	✅
Supports adding arbitrary setup steps (e.g. adding reroute pipeline, resolving migration deprecations etc.)	❌	✅

[raultorrecilla]

@ericywl I see all subissues closed, but I believe there are some pending tasks to do. could you create them and link them here please? I'll move this one to the next iteration meanwhile.

[ericywl]

@raultorrecilla technically this is done, since we implemented all the existing tests. New issues can go to #16267.