[DOC] Update the demo links on the SDK pages

[kolesnikovae]

• Update the Java, Go, Python, Ruby demo link to point to [play.grafana.org].
• Correct the link to the Java examples folder. The reference to the "Java blog post" actually pertains to the README for the "Java examples" page, so I'm removing it.

[github-actions[bot]]

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

[github-actions[bot]]

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

[github-actions[bot]]

The backport to release/v1.5 failed:

Validation Failed: "Could not resolve to a node with the global id of 'T_kwDOAG3Mbc4AczmP'."

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-3240-to-release/v1.5 origin/release/v1.5
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x d111cdf24bfad7753e1467d79e20ce1b05ade96d

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-3240-to-release/v1.5
# Create the PR body template
PR_BODY=$(gh pr view 3240 --json body --template 'Backport d111cdf24bfad7753e1467d79e20ce1b05ade96d from #3240{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title "[release/v1.5] [DOC] Update the demo links on the SDK pages" --body-file - --label "type/docs" --label "backport" --base release/v1.5 --milestone release/v1.5 --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-3240-to-release/v1.5

# Create a pull request where the `base` branch is `release/v1.5` and the `compare`/`head` branch is `backport-3240-to-release/v1.5`.

# Remove the local backport branch
git switch main
git branch -D backport-3240-to-release/v1.5