Move misc-checks logic into openconfig-ci

[wenovus]

Currently, misc-checks is done via file-message-passing to post_results. This is not ideal since message passing via files is less testable and requires more work (annoying to write text files and define the message-passing format), and is as a result more error-prone and makes new checks harder to add.

For example, if I wanted to add a more precise type check for backwards-incompatibilities, then the right place to put it is the openconfig-ci tool breaking-check checker. However I would need to generate a text file in order to merge it with the "Major version updates in commit xx" message so as to not clutter the PR. This adds to the complexity of the CI system.

A better way is to just have a single tool that does all of the openconfig CI checks. Any failures would be recorded, and any messages about potential breaking changes, and "Major version updates in commit xx", or other future informative messages can be recorded there without having to deal with message passing.