Add git init button (#26522)

Because why not

Release Notes:

- N/A

crates/proto/proto/zed.proto

@@ -344,7 +344,9 @@ message Envelope {
         AskPassResponse ask_pass_response = 318;
 
         GitDiff git_diff = 319;
-        GitDiffResponse git_diff_response = 320; // current max
+        GitDiffResponse git_diff_response = 320;
+
+        GitInit git_init = 321; // current max
     }
 
     reserved 87 to 88;
@@ -2937,3 +2939,9 @@ message GitDiff {
 message GitDiffResponse {
     string diff = 1;
 }
+
+message GitInit {
+    uint64 project_id = 1;
+    string abs_path = 2;
+    string fallback_branch_name = 3;
+}

crates/proto/src/proto.rs

@@ -460,6 +460,7 @@ messages!(
     (CheckForPushedCommitsResponse, Background),
     (GitDiff, Background),
     (GitDiffResponse, Background),
+    (GitInit, Background),
 );
 
 request_messages!(
@@ -607,6 +608,7 @@ request_messages!(
     (GitChangeBranch, Ack),
     (CheckForPushedCommits, CheckForPushedCommitsResponse),
     (GitDiff, GitDiffResponse),
+    (GitInit, Ack),
 );
 
 entity_messages!(
@@ -713,6 +715,7 @@ entity_messages!(
     GitCreateBranch,
     CheckForPushedCommits,
     GitDiff,
+    GitInit,
 );
 
 entity_messages!(