Feature request: Support SARIF annotations

It would be awesome to be able to support [SARIF](https://docs.github.com/en/code-security/code-scanning/integrating-with-code-scanning/sarif-support-for-code-scanning) (static analysis) notations in reviewable. The gutter is getting pretty cluttered with the coverage and line-too-long bars, but I'm wondering if there's more that can be done there or in a text highlight with hover text and/or small icons.

Part of the motivation here is to make it easier to run the pre-review cycle where the author creates the PR and then verifies that no regressions or issues have been introduced, but CI is in charge of providing attestation, much like for the code coverage.

As a reviewer, you could imagine that SARIF warnings would cause me to examine the code in question and possibly just LGTM it if the warning is spurious, though I think a healthier pattern would be for authors to then add an exclusion for that specific warning instance so that future reviewers don't re-spend time examining the same warning.

Definitely having warnings visible for an existing codebase as you turn on static analytics tools would be super helpful.