feat: create the initial snapshot (logical case) (#139)

Description

• create the initial snapshot using the existing provision service (the abstraction layer is present)
• add an ability to inject custom pre-processing code
• keep metadata to a file (datastateat, snapshot type)
• retrieve datastateat from a dump:
  • by default use the current timestamp, mark with a special flag
  • direct dump/restore - start timestamp
  • restore from a dump - use pg_restore metadata (pg_restore -l)

Related issue

#139 (closed)

Examples

retrieval:
  stages:
    - initialize
  spec:
    initialize:
        - name: logical-dump
          ...
        - name: logical-restore
          ...
        - name: logical-snapshot
          options:
            scriptBeforeSnapshot: "/tmp/scripts/custom.sh"

Checklist

• the MR description has been reviewed
• this MR contains text changes and they have been reviewed OR there are no texts changes
• this MR contains GUI/CLI changes and they have been reviewed OR there are no GUI/CLI changes
• this MR contains API changes, specifications reflect those changes and they have been reviewed OR there are no API changes

Closes #139 (closed)