Create Patch action

[gsaslis]

After a contributor has made some changes on a git branch, they need to create a patch and submit it for review to the project maintainer.

For reference, here is the CLI experience: https://app.radicle.xyz/nodes/seed.radicle.xyz/rad:z3gqcJUoA1n9HaHKufZs5FCSGazv5/tree/radicle-cli/examples/workflow/4-patching-contributor.md

In essence, we just need a dialog / editor tab where the contributor can insert the patch title and a (markdown-formatted) textarea for the patch description. It could be the same "view" that is used for the overview/activity of an existing patch (but with empty fields, of course).