Clarify precedence for environment variables

[hillaryfraley]

Description

A user recently commented Runtime env_vars defined for a slack handler's definition in backend lose to event's entity annotations if latter are present.

The docs discuss precedence related to environment variables in https://docs.sensu.io/sensu-go/latest/observability-pipeline/observe-schedule/backend/#create-overrides.

Category

This is an issue with:

• errata (error in doc content)
• new doc (requires a completely new doc)
• update (add missing or refresh existing content)
• improvement (improve docs content or format)

Affected pages

https://docs.sensu.io/sensu-go/latest/observability-pipeline/observe-schedule/backend/#create-overrides

Corrections needed

First need to confirm where the clarifications about precedence belong in the docs.

Then, may need to update https://docs.sensu.io/sensu-go/latest/observability-pipeline/observe-schedule/backend/#create-overrides alone, https://docs.sensu.io/sensu-go/latest/observability-pipeline/observe-schedule/backend/#create-overrides in addition to another section in the docs (or a new section), or different sections altogether.

Additional context

HS 28580

[hillaryfraley]

See sensu/sensu-slack-handler#42. I should confirm this is correct (per-entity/per-check annotations always override env vars and handler commands) and if so, add it to https://docs.sensu.io/sensu-go/latest/plugins/assets/

[hillaryfraley]

https://sumologic.slack.com/archives/C024XK35Z3Q/p1652106545499189