Add icon checklist workflow

[Hamster45105]

Description

Basis for this change discussed in #2070

How the action works

When a PR is opened involving icons, github-actions will leave a comment. This comment can be found and edited in .github/icon_checklist.md

Here is an example of it running on a PR: https://github.com/Hamster45105/lawnicons/pull/4

Note

I removed the first_pr_interaction.yml file since it would not really be needed if this action was implemented.

Fixes #2070

Type of change

:x: Bug fix (non-breaking change which fixes an issue) :white_check_mark: General change (non-breaking change that doesn't fit the above categories, such as copyediting)

[Hamster45105]

@x9136 are you happy for me to mark as ready for review now?

[x9136]

are you happy for me to mark as ready for review now?

It's up to you. In any case, someone else will do the code review.

[x9136]

Great job, thanks!