CI: build with -tags stringlabels

[bboreham]

What this PR does

Change the tags used in CI to include stringlabels.
This uses less memory, especially in ingesters. See #3555.

Checklist

• Tests updated
• NA Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[pracucci]

[nit] We've a script parsing CHANGELOG (used during the release process) and I think doesn't parse the numbers correctly with a ,

Suggested change

	* [ENHANCEMENT] Use new data structure for labels, to reduce memory consumption. #3555, #5731
	* [ENHANCEMENT] Use new data structure for labels, to reduce memory consumption. #3555 #5731

[dimitarvdimitrov]

LGTM. There are docs which mention how to run integration tests. I think it's worth changing the instructions to also include stringlabels so that CI and local integration tests run more or less under the same conditions.

mimir/docs/internal/contributing/how-integration-tests-work.md

Lines 15 to 29 in 1d80673

	```
	go test -v -tags=requires_docker ./integration/...
	```
	If you want to run a single test you can use a filter. For example, to only run `TestChunksStorageAllIndexBackends`:
	```
	go test -v -tags=requires_docker ./integration -run "^TestChunksStorageAllIndexBackends$"
	```
	When running all integration tests, the test process may time out before the tests complete. If this happens, you can increase `go test`'s default 10 minute timeout to something longer with the `-timeout` flag, for example:
	```
	go test -v -tags=requires_docker -timeout=20m ./integration/...
	```

[bboreham]

There are docs which mention how to run integration tests. I think it's worth changing the instructions to also include stringlabels so that CI and local integration tests run more or less under the same conditions.

Note it's not too important how the test driver is built; they invoke the image which will have been built with stringlabels.
However I can change the docs if you think consistency is important.

[bboreham]

It would also be good to tell people to add -stringlabels to go test, and to their IDE config for running tests, the debugger, etc.
But I'm not aware of any centralised way to do this.

[dimitarvdimitrov]

There are docs which mention how to run integration tests. I think it's worth changing the instructions to also include stringlabels so that CI and local integration tests run more or less under the same conditions.

Note it's not too important how the test driver is built; they invoke the image which will have been built with stringlabels. However I can change the docs if you think consistency is important.

That's a good point. Happy to leave docs out of this PR