docs: Update labels, add cardinality topic

[JStickler]

What this PR does / why we need it:

Reorganizes and revises the Labels topic to take into account:

• New default service_name label
• Label defaults for OTEL
• Provides additional guidance to help customers avoid known issues with labels

Adds a new topic for cardinality.

[Jayclifford345]

Really great write up on labels and cardinality. These are just a few points I noticed but they are only suggestions :)

[github-actions]

💻 Deploy preview deleted.

[slim-bean]

LGTM!

[loki-gh-app]

This PR must be merged before a backport PR will be created.

[loki-gh-app]

The backport to release-3.3.x 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-15399-to-release-3.3.x origin/release-3.3.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x b5084dcc7f9686ca1500d8d999ebfd08d5c2be59

When the conflicts are resolved, stage and commit the changes:

git add . && git cherry-pick --continue

If you have the GitHub CLI installed:

# Push the branch to GitHub:
git push --set-upstream origin backport-15399-to-release-3.3.x
# Create the PR body template
PR_BODY=$(gh pr view 15399 --json body --template 'Backport b5084dcc7f9686ca1500d8d999ebfd08d5c2be59 from #15399{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title 'docs: Update labels, add cardinality topic (backport release-3.3.x)' --body-file - --label 'size/L' --label 'type/docs' --label 'backport' --base release-3.3.x --milestone release-3.3.x --web

Or, if you don't have the GitHub CLI installed (we recommend you install it!):

# Push the branch to GitHub:
git push --set-upstream origin backport-15399-to-release-3.3.x

# Create a pull request where the `base` branch is `release-3.3.x` and the `compare`/`head` branch is `backport-15399-to-release-3.3.x`.

# Remove the local backport branch
git switch main
git branch -D backport-15399-to-release-3.3.x