S3 support and scaled monolith

[mmkay]

Issue

Add s3 support to tempo charm and scaled monolithic setup in case application is scaled to more than 1 unit. Closes #62, #119

Solution

Add s3 interface that can be used by s3-integrator.

Context

Even though mimir_config is already using types, I haven't switched to typing yet as I expect we'll have more changes with tempo_cluster soon.

Testing Instructions

In theory the following bundle should work, but it still requires manual steps. Follow the steps added in HACKING.md to deploy minio alongside:

bundle: kubernetes
applications:
  minio:
    charm: minio
    channel: latest/edge
    revision: 316
    base: [email protected]/stable
    resources:
      oci-image: 543
    scale: 1
    options:
      access-key: minio-access-key
      secret-key: minio-secret
    constraints: arch=amd64
    storage:
      minio-data: kubernetes,1,10240M
    trust: true
  s3-integrator:
    charm: s3-integrator
    channel: latest/stable
    revision: 17
    scale: 1
    options:
      bucket: tempo
    constraints: arch=amd64
  tempo:
    charm: local:tempo-k8s-1
    scale: 1
    constraints: arch=amd64
    storage:
      data: kubernetes,1,1024M
relations:
- - tempo:s3
  - s3-integrator:s3-credentials

Release Notes

[PietroPasotti]

YESSSS

[mmkay]

two more things still pending from manual tests, not merging yet

[PietroPasotti]

LGTM
note to self: next time, let's keep the formatting changes aside :/

[dimaqq]

Random fly-by review