Proof-of-concept oc access to firing alerts

Implementing RFE-928 would help a number of update-team use-cases:

• OTA-368, OSDOCS-2427, and other tickets that are mulling over rendering update-related alerts when folks are trying to decide whether to launch an update.
• OTA-1021's update status subcommand could use these to help admins discover and respond to update-related issues in their updating clusters.

The updates team is not well positioned to maintain oc access long-term; that seems like a better fit for the monitoring team (who maintain Alertmanager) or the workloads team (who maintain the bulk of oc). But we can probably hack together a proof-of-concept which we could later hand off to those teams, and in the meantime it would unblock our work on tech-preview commands consuming the firing-alert information.

The proof-of-concept could follow the following process:

1. Get alertmanager URL from route alertmanager-main in openshift-monitoring namespace
2. Use the $ALERTMANAGER/api/v1/alerts endpoint to get data about alerts (see https://github.com/prometheus/alertmanager#api)
3. The endpoint is authenticated via bearer token, same as against apiserver (possible Role for this mentioned in MON-3396 OBSDA-530)

Definition of done:

$ OC_ENABLE_CMD_INSPECT_ALERTS=true oc adm inspect-alerts
...dump of firing alerts...

and a backing Go function that other subcommands like oc adm upgrade status can consume internally.