Document event naming convention

For implementation details on adding new events, see the

[analyzer README](https://gitlab.com/gitlab-org/security-products/analyzers/secrets#adding-observability-events).

### Event naming convention

Follow this pattern when adding new events:

```plaintext

collect_<analyzer_name>_<type>_metrics_from_pipeline

```

Where `<type>` describes the category of metrics. For example:

- `collect_secrets_analyzer_scan_metrics_from_pipeline`

- `collect_secrets_analyzer_ruleset_customization_metrics_from_pipeline`

- `collect_ds_analyzer_scan_duration_metrics_from_pipeline`

> [!note]

> Some existing [events](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/app/services/security/process_scan_events_service.rb#L9) use different naming patterns (for example,

> `sast_scan` instead of the analyzer name). These are unchanged

> to avoid breaking existing Snowflake queries and dashboards.

> This convention applies to new events only.

### Register the event

Events require a corresponding definition in the GitLab monolith and must be added to the