Resolve "Add upstream alias to Mimir"

General MR

Summary

• Added upstream alias to mimir-distributed chart dependency to conform with Big Bang passthrough standards.
• Upstream values moved to bottom of values.yaml file
• Corrected README value generation

Umbrella Branch

mimir-passthrough

Relevant logs/screenshots

Linked Issue

issue

Upgrade Notices

All values currently under key mimir-distributed will need to be shifted under the upstream key to conform to new Big Bang passthrough chart standards.

Previous Values:

mimir-distributed:
  image:
    repository: registry1.dso.mil/ironbank/opensource/grafana/mimir
    tag: 2.17.0
    pullSecrets:
    - private-registry
  ...

Current Values:

upstream:
  image:
    repository: registry1.dso.mil/ironbank/opensource/grafana/mimir
    tag: 2.17.0
    pullSecrets:
    - private-registry
  ...

Related to #81 (closed)