Add rgUSD base #800

The pull request embarked with master (d5bc3f3) will be merged soon

Required conditions for merge:

#approved-reviews-by>=1 [🛡 GitHub branch protection]
- #800
#changes-requested-reviews-by=0 [🛡 GitHub branch protection]
- #800
#review-threads-unresolved=0 [🛡 GitHub branch protection]
- #800
branch-protection-review-decision=APPROVED [🛡 GitHub branch protection]
- #800
all of [📃 From pull request rule Automatic merge on approval]:
- -draft [📌 queue requirement]
  - #800
- all of:
  - #approved-reviews-by>=1
    - #800
  - #changes-requested-reviews-by=0
    - #800
  - #review-threads-unresolved=0
    - #800
  - base==master
  - label!=do-not-merge
    - #800
- any of [📌 queue -> configuration change requirements]:
  - -mergify-configuration-changed
    - #800
  - check-success=Configuration changed
- any of [🔀 queue conditions]:
  - all of [📌 queue conditions of queue default]:
    - #approved-reviews-by>=1 [🛡 GitHub branch protection]
      - #800
    - #changes-requested-reviews-by=0 [🛡 GitHub branch protection]
      - #800
    - #review-threads-unresolved=0 [🛡 GitHub branch protection]
      - #800
    - branch-protection-review-decision=APPROVED [🛡 GitHub branch protection]
      - #800