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/close.md

@@ -0,0 +1,18 @@
+# Close a Pull Request
+
+> `n34 pr close` command
+
+**Usage:**
+```
+Usage: n34 pr close [OPTIONS] <PR_ID>
+
+Arguments:
+  <PR_ID>  The open/draft PR id to close it
+
+Options:
+      --repo <NADDR-NIP05-OR-SET>  Repository addresses
+```
+
+Issue a kind `1632` (Close status) for the specified PR. The PR have to be open
+or drafted.
+