[ Docs ] Add note re: nuance re MICRONAUT_ENVIRONMENT scope depending on how TOWER_OIDC_CLIENT value set

[gwright99]

Background

A recent investigation revealed an interesting nuance re: how the OIDC login button presents on the Platform landing page.

• To make the button appear, the backend container's MICRONAUT_ENVIRONMENTS variable must contain the scope auth-oidc.
• Platform code will automatically add this scope if it detects the TOWER_OIDC_CLIENT environment variable within the backend container.
• In the CX Installer project, we bundle all the TOWER_OIDC_* values as SSM entries (for convenience). Since this value is being sourced at runtime, it does NOT appear as an environment variable and thus this is why we have to explicitly set the scope via code.

TODOs

• Add note in project explaining this mechanism.
• Consider removing this value from cron since it's not necessary.
• Cleanup edgecase that was noticed where ,, gets appended to the end of MICRONAUT_ENVIRONMENTS when no OIDC is active.