[#21381] Tools: Set LC_ALL=C.UTF-8 when running pgrep in yb-ctl

Summary:
When other processes have UTF-8 characters in their names, pgrep may fail
due to expecting a different encoding.

This revision fixes the issue by setting
the `LC_ALL` environment variable to `C.UTF-8` when invoking `pgrep`. Note that
the environment variable is only set for the subprocess which `pgrep` runs in;
this change does not modify it anywhere else.
Jira: DB-10275

Test Plan:
```
bin/yb-ctl create
```

Reviewers: mbautin

Reviewed By: mbautin

Differential Revision: https://phorge.dev.yugabyte.com/D33008

scripts/installation/bin/yb-ctl

@@ -1284,7 +1284,8 @@ class ClusterControl:
                 pgrep_full_command_output_arg = '--list-full'
             pgrep_regex_str = self.get_pgrep_regex(daemon_id)
             pgrep_output = subprocess.check_output(
-                ["pgrep", pgrep_full_command_output_arg, "-f", pgrep_regex_str]
+                ["pgrep", pgrep_full_command_output_arg, "-f", pgrep_regex_str],
+                env={"LC_ALL": "C.UTF-8"}
             ).strip().decode('utf-8')
 
             data_dirs_re_match = FS_DATA_DIRS_ARG_RE.search(pgrep_output)