[ghc] add automation

[ulidtko]

Followup to endoflife-date/endoflife.date#6287, adds integration for the thing to keep rolling more-or-less autonomously (without regular mandatory attention).

A new script within existing framework.

• Parses the source table from wiki
• Fills out releases
• Fixes versions dates to come from wiki tables, rather than git tags (formal version announcements sometimes precede git tag, sometimes lag behind).

I understood that

--- i/products/ghc.md
+++ w/products/ghc.md
@@ -22,6 +22,7 @@ auto:
   - git: https://gitlab.haskell.org/ghc/ghc.git
     regex: ^ghc-(?P<major>\d+)[.](?P<minor>\d+)[.](?P<patch>\d+)-release$
     template: '{{major}}.{{minor}}.{{patch}}'
+  - custom: ghc-wiki
 
 releases:

plus a submodule bump (maybe?), will be needed as another follow-up in the main repo.

✔️ Tested locally. (Thence the diff in generated json)

[ulidtko]

@captn3m0 @marcwrobel please review, if/when time permits