refactor(ci): introduce meta backend agnostic e2e tests #19568

3 / 4 tasks completed

1 task still to be completed

Task	Status
Change `meta-backend` to `env` for `ci-3streaming-2serving-3fe`, so that we can use this single profile for running e2e tests against 3 backends.	Incomplete
Based on above, introduce a build matrix for all 3 backends and their endpoints to merge end-to-end tests against 3 backends in `main-cron`.	Incomplete
For `pull-request`, only MySQL and Postgres are included in the matrix since I still want to make it optional to run tests against them, which was triggered by PR label `ci/run-e2e-test-other-backends`.	Incomplete
I have written necessary rustdoc comments	Completed
I have added necessary unit tests and integration tests	Completed
All checks passed in `./risedev check` (or alias, `./risedev c`)	Completed
My PR needs documentation updates. (Please use the Release note section below to summarize the impact on users)	Incomplete
#19595	Incomplete
#19568 👈 (View in Graphite)	Incomplete
#19560	Incomplete
`main`	Incomplete