Feat: Adds Ability to Merge MR (#147)

This adds the ability to merge an MR from within `gitlab.nvim` directly. If the reviewer is open, it'll be closed automatically. Users may configure whether they'd like to squash commits on the merge, as well as whether they'd like to delete the original source branch on a merge.

If squashing, users are prompted to provide an optional custom squash message for the squash commit.

README.md

@@ -23,6 +23,7 @@ https://github.com/harrisoncramer/gitlab.nvim/assets/32515581/dc5c07de-4ae6-4335
 - [Usage](#usage)
   - [The summary command](#summary)
   - [Reviewing Diffs](#reviewing-diffs)
+  - [Merging](#merging-an-mr)
   - [Discussions and Notes](#discussions-and-notes)
   - [Discussion signs and diagnostics](#discussion-signs-and-diagnostics)
   - [Uploading Files](#uploading-files)
@@ -131,6 +132,7 @@ require("gitlab").setup({
     note = nil,
     pipeline = nil,
     reply = nil,
+    squash_message = nil,
   },
   discussion_tree = { -- The discussion tree that holds all comments
     auto_open = true, -- Automatically open when the reviewer is opened
@@ -210,6 +212,10 @@ require("gitlab").setup({
     success = "✓",
     failed = "",
   },
+  merge = { -- The default behaviors when merging an MR, see "Merging an MR"
+    squash = false,
+    delete_branch = false,
+  },
   colors = {
     discussion_tree = {
       username = "Keyword",
@@ -258,6 +264,19 @@ require("gitlab").create_comment_suggestion()
 
 For suggesting changes you can use `create_comment_suggestion` in visual mode which works similar to `create_multiline_comment` but prefills the comment window with Gitlab's [suggest changes](https://docs.gitlab.com/ee/user/project/merge_requests/reviews/suggestions.html) code block with prefilled code from the visual selection.
 
+### Merging an MR
+
+The `merge` action will merge an MR. The MR must be in a "mergeable" state for this command to work.
+
+```lua
+require("gitlab").merge()
+require("gitlab").merge({ squash = false, delete_branch = false })
+```
+
+You can configure default behaviors via the setup function, values passed into this function will override the defaults.
+
+If you enable `squash` you will be prompted for a squash message. To use the default message, leave the popup empty. Use the `settings.popup.perform_action` to merge the MR with your message.
+
 ### Discussions and Notes
 
 Gitlab groups threads of comments together into "discussions."
@@ -391,6 +410,7 @@ vim.keymap.set("n", "glra", gitlab.add_reviewer)
 vim.keymap.set("n", "glrd", gitlab.delete_reviewer)
 vim.keymap.set("n", "glp", gitlab.pipeline)
 vim.keymap.set("n", "glo", gitlab.open_in_browser)
+vim.keymap.set("n", "glM", gitlab.merge)
 ```
 
 ## Troubleshooting