feat: add Grove maintenance pages

Description

This PR adds the necessary changes to enable Maintenance Pages on Grove as per this discovery

Testing instructions

• Read through the code and check that it makes sense
• Further instructions will be in a linked PR. grove!101 (merged)

Other information

How do the maintenance pages work?

Assuming your instance name is lemington

We enable maintenance mode by:

• Deleting the ingress resources created by Grove under the lemington namespace.
• Once done, create a new namespace lemington-maintenance. Under this namespace:
  • Create a caddy pod that will serve the maintenance files
  • Create a new ingress for the lms/studio domains that point to this caddy instance.

Disabling maintenance mode is similar:

• Delete the lemington-maintenance namespace (which will delete all associated resources)
• Apply the ingress manifest again for the lms, studio et. al.