chore: prepare for release 0.5.1-rc1

[sam-berning]

Description of changes:

Prepare changelog and bump version

Testing done

• Built core-kit and AMI with twoliter
• Tested AMI build on a system affected by https://github.com/bottlerocket-os/twoliter/issues/403

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.