Update CHANGELOG and composer version for v1.0.0 release

[unfulvio-godaddy]

Note ⚠️ PLEASE NOTE THIS SHOULD BE MERGED RIGHT BEFORE TAGGING v1.0.0

Summary

This PR updates the following prior to tagging v1.0.0

• CHANGELOG.md entry
• composer.json version is bumped to 1.0.0 (note: the 9.6 reference to PHPUnit doesn't require composer update because PHPUnit is already to 9.6 in lock file)

Closes: #229

Details

Contributor checklist

• [x] I agree to follow this project's Code of Conduct.
• [x] I have updated the documentation accordingly
• [ ] I have added tests to cover changes introduced by this pull request
• [ ] All new and existing tests pass

Testing

n/a - no functionality change

Reviewer checklist

- [ ] There are no other outstanding PRs other than this one - [ ] The team has agreed to tag v1.0.0 - [x] Code changes review - [ ] Documentation changes review - [x] Unit tests pass - [x] Static analysis passes

[coveralls]

coverage: 65.513%. remained the same when pulling 6ecaf7493be4392e2c50229834702def82598f38 on chore/update-items-for-v1.0.0-release into 7a4cc8ffebcde1a2048a576094d38befb0e77f48 on trunk.