feature request: minimal PR description option/formatting

Right now, Dependabot fills the PR description with HTML. This provides a very pretty PR in the Github UI, but plays poorly with git workflows that use the PR description when that PR is merged. We end up with commit messages that look like this:


This is from https://github.com/tendermint/tendermint/commit/ad9003d448abdb1aeb105025fceb683198ffac7b. If you scroll down, you can even see that the commit message has Dependabot usage instructions in there!

**It would be awesome to have a formatting option to use plaintext or even markdown for the PR body, and even more awesome to have a "minimal" option that didn't include Dependabot instructions and other superfluous stuff.** This seems similar to https://github.com/dependabot/feedback/issues/287, but not exactly.

Thanks y'all! My team loves Dependabot, and we'd love to see it get even better!

The issue names no files, tests, or entry points. Start by locating the Dependabot code that assembles GitHub PR descriptions, then determine how formatting and minimal-content options should be represented and tested; done means users can choose plaintext or Markdown and omit the extra instructions and other superfluous content.

Written by the indexing model from the issue text.