Merge pdbq:add-collect-watch into pdbq:main

I've used a bash script, ./scripts/watch-query, to scan for new upstream versions. The info it collects then feeds into the tools used to make the merge board, as well as the merge opportunities email.

This completes a rewrite of that bash script to python, and refactors things to be a bit more pythonic. I will probably do a bit more hacking on it before setting up the cronjob for it, but it's at a good stage for reviewing.

For a bit of extra context, for Pdbq 'workers' are intended to be run as discrete jobs to pull data from remote sites and re-process it into JSON records. This is not the first worker script for Pdbq but my objective is to make this one fully fleshed out so it can serve as an example of a "finished" worker. So, review comments to cleanup the style or fix the syntax or to simplify the code would be much appreciated.

There is a smoketest:

  $ ./workers/collect-watch --test
  Retrieved information for package:
  {'debian-mangled-uversion': '2.10',
   'debian-uversion': '2.10',
   'package': 'hello',
   'status': 'newer package available',
   'upstream-url': 'https://ftp.gnu.org/gnu/hello/hello-2.12.1.tar.gz',
   'upstream-version': '2.12.1'}

  Expected:
  {'debian-mangled-uversion': '2.10',
   'debian-uversion': '2.10',
   'package': 'hello',
   'status': 'newer package available',
   'upstream-url': 'https://ftp.gnu.org/gnu/hello/hello-2.12.1.tar.gz',
   'upstream-version': '2.12.1'}

  output matches example

For a regular run, create a /tmp/input.json file with contents like this:

  {
      "source_package_name": "dovecot",
      "checkouts_dir": "/tmp",
      "watch_override": null,
      "logging": false
  }

Then run:

  $ ./workers/collect-watch /tmp/dovecot.json
  {
      "contents": {
          "component": "\n",
          "debian-mangled-uversion": "2.3.19.1",
          "debian-uversion": "2.3.19.1+dfsg1",
          "package": "dovecot",
          "status": "newer package available",
          "upstream-url": "https://dovecot.org/releases/2.3/dovecot-2.3.20.tar.gz",
          "upstream-version": "2.3.20"
      },
      "date_collect_finished": "Fri Mar 17 00:24:36 2023",
      "date_collect_started": "Fri Mar 17 00:22:22 2023",
      "source_package": "dovecot"
  }