functionaltests: 7.x standalone -> 8.x standalone -> 9.x standalone -> 9.x managed

[ericywl]

As per #16180, we need to reindex the data streams and indices before upgrading to 9.0+ version. The new steps would then be:

1. Create 7.x standalone, ingest and check
2. Upgrade to 8.x standalone, ingest and check
3. Query deprecation warnings from ES, and perform reindexing / block writing to indices
4. Upgrade to 9.x standalone, ingest and check
5. Upgrade to 9.x managed, ingest and check

[endorama]

Q: is not clear to me why step 3 (Query deprecation warnings from ES, and perform reindexing / block writing to indices) only applies to standalone or it only applies to 9.1.0.

[endorama]

Additional question: as we are reacting to ES migration deprecation logs, should we consider including this in our tests? For example if there are unaddressed deprecations, we may need to act on them either to make the test work or because they affect APM.

[ericywl]

Q: is not clear to me why step 3 (Query deprecation warnings from ES, and perform reindexing / block writing to indices) only applies to standalone or it only applies to 9.1.0.

It applies to all 9.0+ versions I believe.

Additional question: as we are reacting to ES migration deprecation logs, should we consider including this in our tests? For example if there are unaddressed deprecations, we may need to act on them either to make the test work or because they affect APM.

Yes, I believe that's the intent. Maybe we can limit the ones we address to critical deprecation only.