ref(perf-issues): Add projectoption for enabling individual detector (#…

…41328)

### Summary
The settings for detectors are too complicated and we only really want
to expose a simple toggle. I plan on adding this new project option and
removing the old project option settings for independent threshold
changes, to make this system a little more simple. Basically all
detectors will have their issue creation gated by a series of project
options booleans.

src/sentry/projectoptions/defaults.py

@@ -104,3 +104,6 @@
         "n_plus_one_db_duration_threshold": 500,
     },
 )
+
+# Using simple bools instead of rates for disabling individual detectors
+register(key="sentry:performance_issue_creation_enabled_n_plus_one_db", default=True)