Add kafka SASL plain authentication support

[pracucci]

What this PR does

Add SASL plain authentication support to Kafka client both to Mimir and kafkatool. I also manually tested these changes.

Which issue(s) this PR fixes or relates to

N/A

Checklist

• Tests updated.
• Documentation added.
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• about-versioning.md updated with experimental features.

[tacole02]

Thank you!

[dimitarvdimitrov]

sgtm

[gotjosh]

LGTM, great job - simple and clean!

[gotjosh]

nit: I'm not sure which patterns we follow and if its common that when requiring multiple config to be set it basically no-ops unless you set them all. The flag documentation is very clear that you need both hence why this is a nit, but...

I can see from the library that:

	if auth.User == "" || auth.Pass == "" {
		return nil, nil, errors.New("PLAIN user and pass must be non-empty")
	}

hence the reasoning behind not setting it unless you get both, but I wonder if it's convenient to validate that here or let the error bubble up.

I'll leave the decision in your hands and this is considered a very nitpicky nit.

[pracucci]

I think we can add a validation in our config. Let me do it.

[pracucci]

Done in 8cef267

[gotjosh]

LGTM

[grafanabot]

The backport to r310 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-9584-to-r310 origin/r310
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 42284e756e4f6c10d9111444fe4cb53c138ce3e6
# Push it to GitHub
git push --set-upstream origin backport-9584-to-r310
git switch main
# Remove the local backport branch
git branch -D backport-9584-to-r310

Then, create a pull request where the base branch is r310 and the compare/head branch is backport-9584-to-r310.

[grafanabot]

The backport to r311 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-9584-to-r311 origin/r311
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 42284e756e4f6c10d9111444fe4cb53c138ce3e6
# Push it to GitHub
git push --set-upstream origin backport-9584-to-r311
git switch main
# Remove the local backport branch
git branch -D backport-9584-to-r311

Then, create a pull request where the base branch is r311 and the compare/head branch is backport-9584-to-r311.