Append resource links to staging PRs

[HebaruSan]

Motivation

This staging reason explicitly mentions "the forum thread" but fails to provide it:

KSP-CKAN/CKAN-meta#2460

That makes these PRs somewhat annoying to review, since you have to find that link yourself (probably via the status page or by checking the metadata).

Changes

Now we append a table of the mod's resources links to the body of any staging pull request:

KSP-CKAN/CKAN-meta#2462 (manually inserted)

Behind the scenes:

• We add a new, later Netkan transformer because StagingTransformer has to run before the $kref processors to be able to detect hard coded versions, but we usually only have the resources available after those transformers run
• We use Markdown's <link> syntax for links because otherwise GitHub excludes a trailing * from the URL, which we use to abbreviate a lot of forum URLs
• Auto-epoch PRs are affected as well, which should be fine
• --debug prints the Markdown source of the table in case you want to see it

[techman83]

I think that's super sensible. Lgtm!

[DasSkelett]

Agree, very useful; also appears to be working fine!