Let DAMRS_CONFIG name a config file without breaking the load

Let DAMRS_CONFIG name a config file without breaking the load damd and dam-worker both take the path to their config file from DAMRS_CONFIG. That variable sits under the prefix the environment provider scans, so figment offered it as a key named `config`, strict extraction rejected it as an unknown field, and setting the variable that names the config file was the one thing guaranteed to stop either process from starting. Neither binary could be configured by file at all; only damctl was unaffected, because it takes a flag instead. Ignore CONFIG in the env provider. Found by starting the worker against a real database. Nothing in the suite would have caught it: every existing test builds config in-process, so the one path a deployment actually uses was the one path never exercised. The regression test sets the variable and asserts the file's values land.