feat: support pull requests

Support for pull requests, it's not standard in NIPs yet[1] but there must be
two clients that support it to be included in NIPs, n34 is one of them.

This support:
- Create a new PR `n34 pr new`
- Update PR tip `n34 pr update`
- View a PR `n34 pr view`
- List PRs `n34 pr list`
- Add `PR` and `PR-update` kinds as roots in `NostrClient::find_root`
- Support issuing statuses for PRs
- Support GRASP PR and PR-update
- Update the docs

[1] https://github.com/nostr-protocol/nips/pull/1966

docs/pr/update.md

@@ -0,0 +1,25 @@
+# Update a Pull Request
+
+> `n34 pr update` command
+
+**Usage:**
+```
+Usage: n34 pr update [OPTIONS] <EVENT-ID> <COMMIT> <CLONES>...
+
+Arguments:
+  <EVENT-ID>   Original PR ID
+  <COMMIT>     The SHA-1 hash of the commit at the tip of the PR branch
+  <CLONES>...  Repositories to clone for the pull request, separated by commas
+
+Options:
+      --repo <NADDR-NIP05-OR-SET>  Repository addresses
+      --grasp                      Push the pull request update to the repository GRASP server
+```
+
+Update an existing pull request with the new changes.
+
+Utilize the `--grasp` option if you intend to send the pull request to the
+[GRASP] servers. Note that `n34` will not automatically send the pull request
+for you but will indicate where to push your changes.
+
+[GRASP]: https://ngit.dev/grasp