docs: Publish Cortex v1.20.0 release blog post

[shri3016]

What this PR does

Publishes a blog post announcing Cortex v1.20.0 release, highlighting major new features and their benefits for Cortex users.

The blog post covers:

• Prometheus Remote Write 2.0 support (experimental)
• Parquet format support for storage (experimental)
• Advanced query federation with regex tenant resolver
• gRPC stream push for distributor-ingester communication
• Enhanced native histogram support
• Resource-based monitoring and limiting
• UTF-8 name validation support

This helps inform the Cortex community about the significant improvements and capabilities introduced in v1.20.0.

Which issue(s) this PR fixes

Fixes #7104

Checklist

• Documentation added (blog post)
• Tests updated (N/A - documentation only)
• CHANGELOG.md updated (N/A - documentation only)

[shri3016]

Hi @yeya24 ,This is my first PR to Cortex which fixes #7104
Can you or anyone from your team please review this and let me know if there's anything else needed from my side or if any changes are required. Thanks!

[shri3016]

Thanks @yeya24 for allowing the workflow run,I can see that 3 tests are failing,can you guide on what is to be done from my side? Thank you!

[yeya24]

Probably just my personal opinion but I think we should probably dive deeper here. This blog post seems similar to the release post we did

[shri3016]

Thanks for the feedback @friedrichg and @yeya24
I’ve removed the quantitative cost-savings claim and updated the wording to focus on query performance and storage footprint without specific numbers.
Please let me know if this revision looks good or if you’d like any further adjustments.Thanks!

[yeya24]

Again I feel this is just rewriting what we have from the changelog and it is too shallow to me.
I'd expect we dive deeper to those features and adding screenshots, etc. Instead of just calling them out.