feat: //ci/githubstats:query: add --columns option

[basvandijk]

Sometimes we're not interested in certain columns, especially when posting the result of a query to slack which has a limited width. In the past I had to manually trim the result so that it would fit. This adds a --columns option to specify which columns to display or hide.

$ bazel run //ci/githubstats:query -- top --help
...
  --columns COLS        Comma-separated list of columns to display in order or exclude (if preceded by -). Available columns:
                        label,total,non_success,flaky,timeout,fail,non_success%,flaky%,timeout%,fail%,impact,duration_p90,owners (default: None)

$ bazel run //ci/githubstats:query -- last --help
...
  --columns COLS        Comma-separated list of columns to display in order or exclude (if preceded by -). Available columns:
                        last_started_at,duration,status,branch,PR,commit,buildbuddy,errors (default: None)