metrics: gen-metrics command does not collect all possible metrics

**Describe the problem**
After some discussion, it seems that the `cockroach gen metric-list` command is meant to capture and document all possible metrics which can be omitted by the system, but as it stands currently this isn't the case. Metrics like `security.certificate.*` and `seconds_until_enterprise_license_expiry` do not appear in the [metrics page](https://www.cockroachlabs.com/docs/stable/metrics

**To Reproduce**
To validate this, you can run `cockroach gen metric-list | grep security` to verify that no security metrics are captured.
lem.

**Environment:**
- Current master [8e43568](https://github.com/cockroachdb/cockroach/commit/8e435684b2cb63498cc817a347bfd8c4ae426c16)
- OSX

**Additional context**
Unsure the exact % right now, but as it stands the discoverability and documentation of some metrics in the system is hampered by this.

Jira issue: CRDB-42864