Fixes #39 -- Allows date filtering

Fixes #39 (closed) -- Allows user to specify a before and after date in which to collect /var/log/gitlab log files (and tarballs). If only before is specified, then after is presumed to be the beginning of the epoch. If only after is specified, then before is presumed to be now.

In terms of performance, specifying a date runs just as quickly as without one.

Heavily borrowed from @kenneth's MR: https://gitlab.com/gitlab-com/support/toolbox/gitlabsos/-/compare/master...date-selector-gitlab-logs?from_project_id=10948395&straight=false