Updated README to show Messages is GA

[dragonmantank]

Description

Updates the support table to show Messages is supported and GA

Motivation and Context

The table was out of date

Testing Details

N/A

Example Output or Screenshots (if appropriate)

N/A

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov-commenter]

Codecov Report

Merging #713 (b66d8f0) into 2.x (69a40ab) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##              2.x     #713   +/-   ##
=======================================
  Coverage   75.89%   75.89%           
=======================================
  Files          52       52           
  Lines        1282     1282           
=======================================
  Hits          973      973           
  Misses        309      309           

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