Filter out small documentation improvements in changelogs

[BD103]

it's kinda annoying that the bevy changelog includes all the tiny docs PRs

i want to know what changed in the ECS, but much of the A-ECS changelog is stuff like "clarify the purpose of commands in docs" (which changes 1 word), "fix typo in comment", ...

From @inodentry on Discord

Here are a few ideas:

• Label PRs with something like Changelog-Irrelevant and filter them out in generate-release
  • They can either be removed entirely, or added to their own section.
• Remove these small changes retroactively, after the initial changelog has been released
  • Suggested on Discord
• Potentially link to the Github diff, such as 0.12.0...0.13.0, for a full full changelog

[rparrett]

The changelog is currently broken into sections by A-(Area) labels.

I would propose treating PRs labeled with C-Docs as a separate Docs section. This is doable without marking PRs as "irrelevant" or leaving any contributions out of the changelog.