Add release note for ARC 0.27.0

[mumoshu]

We're going to cut the new 0.27.0 release next week, and here's the release note that is intended to cover all the significant features and fixes included in it.

[toast-gear]

Add in a note about the new ubuntu 22.04 runner images. The images aren't tied to v0.27.0 release itself so we'd need to sort of indicate that but it might be nice to highlight the fact they are a thing now and the UID and GID changes.

[ajschmidt8]

any updates on when this new release will be published?

[Link-]

An idea to consider, now that we have https://github.com/actions/actions-runner-controller/discussions/categories/announcements maybe we could also create an announcement there for this release?

[mumoshu]

@Link- Great idea! Shall we start by creating an announcement by copy-pasting the 0.27.0 release note and adding tweaks and corrections on demand?

[mumoshu]

Thanks for reviewing @TingluoHuang! Merging this now so that we have fewer things to do on Monday, which is the day we are planning to finally cut 0.27.0!