Datastructures

config
- user provided configuration, is potentially updated either on startup or by set config rpc
- configures
  - repos - a list of restic repos to which data may be backed up
  - plans - a list of backup plans which consist of
    - directories
    - schedule
    - retention policy
cache
- the cache is a local cache of the restic repo's properties e.g. output from listing snapshots, etc. This may be held in ram or on disk? TBD: decide.
state
- state is tracked plan-by-plan and is persisted to disk
  - stores recent operations done for a plan e.g. last backup, last prune, last check, etc.
  - stores status and errors for each plan
  - history is fixed size and is flushed to disk periodically (e.g. every 60 seconds).
- the state of a repo is the merge of the states of the plans that reference it.