Better handle bugzilla "Web Compatibility" issues in generate-bugzilla-triage-csv

Currently we only get the bugzilla category information for bugzilla bugs with a target milestone set. As such, we miss any bugs that have no milestone set. Instead, these are picked up from the git log instead and are missing the corresponding bugzilla metadata, so end up as "Unknown" in the generated CSV.

A large chunk of these "Unknown" bugs are from the "Web Compatibility" product category, but are mixed among the other "Unknown" issues. I guess because this is implemented as a webcompat system extension in Firefox, that's why they don't set milestones, I'm really not sure.

It would be helpful if these web compatibility issues could be grouped together to make the review easier to parse.

I think either we could:

1. Find a way to fetch the bugzilla metadata for these "Unknown" bugs.
2. Split out the "Web Compatibility" product bugs, and similar milestone-less components, into a separate review.
3. Filter out "Web Compatibility" bugs from the git log. On the one hand, this may be safe to filter out because we do not use the webcompat extension in Tor Browser. However, I'm not sure whether this product contains issues that may still be relevant to us, so should still be reviewed. Moreover, reviewing these bugzilla issues still led to me open an issue for the firefox privacy team, even though it wasn't relevant to Tor Browser.

/cc @morgan