Add 'operator migrate-algolia-to-postgresql' command

[jfreda]

This PR adds a new hermes operator migrate-algolia-to-postgresql command that migrates all data from Algolia to PostgreSQL. In v1 of the API, Algolia was used as the source of truth, but this will change to PostgreSQL for all non-search data in v2 of the API (which is currently behind a feature flag) — this command enables a migration path for v1 to v2.

New commands:

$ hermes operator -help
Usage: hermes operator <subcommand> [options] [args]

  This command groups subcommands for operators interacting with Hermes.

Subcommands:
    migrate-algolia-to-postgresql    Migrate Algolia data to PostgreSQL

$ hermes operator migrate-algolia-to-postgresql -help
Usage: hermes operator migrate-algolia-to-postgresql

  This command migrates document data from Algolia to PostgreSQL.

Command Options:
  -auto-approve
    	Skip interactive approval for updating documents.
  -config string
    	(Required) Path to Hermes config file
  -dry-run
    	Only print the changes to PostgreSQL data instead of updating the data.
  -verbose
    	Print extra information.