cli: Add 'sentry extract-scheduler-tasks' command

Usage: swh sentry extract-scheduler-tasks [OPTIONS]

  Extract scheduler task parameters from events.

  This command allows to extract scheduler task parameters from Sentry events
  related to a Software Heritage scheduler task and dumps a CSV file to stdout
  that can be consumed by the CLI command:

  $ swh scheduler task schedule --columns type --columns kwargs <csv_file>.

Options:
  -u, --sentry-url TEXT           Sentry URL  [default:
                                  https://sentry.softwareheritage.org]
  -t, --sentry-token TEXT         Bearer token required to communicate with
                                  Sentry API (can also be provided in
                                  SENTRY_TOKEN environment variable)
                                  [required]
  -i, --sentry-issue-number TEXT  Sentry issue number to extract origin URLs
                                  from its events  [required]
  -e, --environment TEXT          Filter on environment: production or
                                  staging, both are selected by default
  -h, --help                      Show this message and exit.