Update changelog.md for Azure Monitor

[steve-tsdb]

Describe your changes

Update changelog to note support for Azure Monitor

Related Issues

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Checklist before requesting a review

• - Is this ready for review? If not, raise as a draft PR
• - This has deployed to a staging environment correctly
• - I have reviewed my changes.
• - I have confirmed the content is technically accurate.
• - I have confirmed the content is free of typos or grammar errors.
• - I have reviewed the deployed version of my changes.
• - I have tested any code that is added or updated.
• - I have verified all images and videos are clear, with appropriate zoom.
• - I have verified all images and videos match production (or dev for unreleased features).
• - I have tested that the content matches the functionality in production (or dev for unreleased features).
• - All checks have passed.
• - This references a feature that is public. If not, add a note and we can schedule the merge for after the feature release.

[github-actions]

Allow 10 minutes from last push for the staging site to build. If the link doesn't work, try using incognito mode instead. For internal reviewers, check web-documentation repo actions for staging build status. Link to build for this PR: http://docs-dev.timescale.com/docs-azure-monitor-changelog