chore: add tool name to mcp metrics (#413)

- [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

PR in `semgrep-proprietary`​:
semgrep/semgrep-proprietary#4810

Author: liukatkat

semgrep_metrics.atd

@@ -291,6 +291,7 @@ type mcp = {
     ?git_username <ocaml mutable>: string option;
     ?git_repo <ocaml mutable>: string option;
     ?git_branch <ocaml mutable>: string option;
+    ?tool_name <ocaml mutable>: string option;
 }
 
 (*****************************************************************************)

semgrep_metrics.py

@@ -919,6 +919,7 @@ class Mcp:
     git_username: Optional[str] = None
     git_repo: Optional[str] = None
     git_branch: Optional[str] = None
+    tool_name: Optional[str] = None
 
     @classmethod
     def from_json(cls, x: Any) -> 'Mcp':
@@ -935,6 +936,7 @@ def from_json(cls, x: Any) -> 'Mcp':
                 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,
+                tool_name=_atd_read_string(x['tool_name']) if 'tool_name' in x else None,
             )
         else:
             _atd_bad_json('Mcp', x)
@@ -963,6 +965,8 @@ def to_json(self) -> Any:
             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)
+        if self.tool_name is not None:
+            res['tool_name'] = _atd_write_string(self.tool_name)
         return res
 
     @classmethod