[8.x](backport #40936) [filebeat][azure-blob-storage] - Simplified state checkpoint calculation

[mergify]

Type of change

• Enhancement

Proposed commit message

• WHAT: Simplified state checkpoint calculation
• WHY: The existing state checkpoint calculation logic was convoluted and depended on unreliable flag logic, then it has been simplified so that if errors occur they are become simpler to debug.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes Simplify azure-blob storage state logic computation #40674

Use cases

Screenshots

Logs

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This is an automatic backport of pull request #40936 done by [Mergify](https://mergify.com).

[botelastic]

This pull request doesn't have a Team:<team> label.

[mergify]

This pull request has not been merged yet. Could you please review and merge it @ShourieG? 🙏

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b mergify/bp/8.x/pr-40936 upstream/mergify/bp/8.x/pr-40936
git merge upstream/8.x
git push upstream mergify/bp/8.x/pr-40936