[ADR] Select a credential rotation solution for Mattermost

[Racer159]

Is your feature request related to a problem? Please describe.

As Ashton I want to be able to rotate Mattermost credentials safely so that I can meet IA requirements and build a more secure system.

Describe the solution you'd like

We should determine a way to automate the rotation of credentials for Mattermost so that we can reduce the cognitive load in doing these rotations. This should include:

• K8s secrets
• CA certificates
• Admin account creds
• RDS and any hard creds for dependencies

These should be written in a simple ADR to capture why the final solution was chosen and a follow on implementation issue should be created.

Additional context

This is needed to meet IA requirements and we should do this in as automated a way as possible likely using Zarf, UDS CLI or Pepr.

[oates]

needs spike

[Racer159]

blocked on defenseunicorns/uds-software-factory#45