chore: add git into to mcp metrics (#410)

- [x] I ran `make setup && make` to update the generated code after editing a `.atd` file (TODO: have a CI check)
- [x] I made sure we're still backward compatible with old versions of the CLI.
For example, the Semgrep backend need to still be able to _consume_ data
generated by Semgrep 1.50.0.
See https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades
Note that the types related to the semgrep-core JSON output or the
semgrep-core RPC do not need to be backward compatible!
- [ ] Any accompanying changes in `semgrep-proprietary` are approved and ready to merge once this PR is merged

Author: liukatkat

semgrep_metrics.atd

@@ -278,6 +278,7 @@ type finding = {
   severity: string;
 }
 
+
 type mcp = {
     ?session_id <ocaml mutable>: string option;
     ?num_skipped_rules <ocaml mutable>: int option;
@@ -287,6 +288,9 @@ type mcp = {
     ?findings <ocaml mutable>: (string (* rule_id *) * finding) list <json repr="object"> option;
     ?errors <ocaml mutable>: string list option;
     ?num_lines <ocaml mutable>: int option;
+    ?git_username <ocaml mutable>: string option;
+    ?git_repo <ocaml mutable>: string option;
+    ?git_branch <ocaml mutable>: string option;
 }
 
 (*****************************************************************************)

semgrep_metrics.py

@@ -916,6 +916,9 @@ class Mcp:
     findings: Optional[List[Tuple[str, Finding]]] = None
     errors: Optional[List[str]] = None
     num_lines: Optional[int] = None
+    git_username: Optional[str] = None
+    git_repo: Optional[str] = None
+    git_branch: Optional[str] = None
 
     @classmethod
     def from_json(cls, x: Any) -> 'Mcp':
@@ -929,6 +932,9 @@ def from_json(cls, x: Any) -> 'Mcp':
                 findings=_atd_read_assoc_object_into_list(Finding.from_json)(x['findings']) if 'findings' in x else None,
                 errors=_atd_read_list(_atd_read_string)(x['errors']) if 'errors' in x else None,
                 num_lines=_atd_read_int(x['num_lines']) if 'num_lines' in x else None,
+                git_username=_atd_read_string(x['git_username']) if 'git_username' in x else None,
+                git_repo=_atd_read_string(x['git_repo']) if 'git_repo' in x else None,
+                git_branch=_atd_read_string(x['git_branch']) if 'git_branch' in x else None,
             )
         else:
             _atd_bad_json('Mcp', x)
@@ -951,6 +957,12 @@ def to_json(self) -> Any:
             res['errors'] = _atd_write_list(_atd_write_string)(self.errors)
         if self.num_lines is not None:
             res['num_lines'] = _atd_write_int(self.num_lines)
+        if self.git_username is not None:
+            res['git_username'] = _atd_write_string(self.git_username)
+        if self.git_repo is not None:
+            res['git_repo'] = _atd_write_string(self.git_repo)
+        if self.git_branch is not None:
+            res['git_branch'] = _atd_write_string(self.git_branch)
         return res
 
     @classmethod