Introduce global OCIS_EVENTS_ENDPOINT and OCIS_EVENTS_CLUSTER

[mmattel]

We have many servcies that use local envvars like:
AUDIT_EVENTS_ENDPOINT and AUDIT_EVENTS_CLUSTER
but not global ones.

For ease of configuration, we should add global envvars:
OCIS_EVENTS_ENDPOINT and OCIS_EVENTS_CLUSTER

Just run a grep in the services folder like grep -rl _EVENTS_ENDPOINT and you get the list of services affected.

Idea mentioned by @butonic in PR #5846 (Antivirus)

@butonic @kobergj @micbar