[New Feature]: Synchronise the multiple terms used for the same licences (e.g. for GPL)

### Description of the new feature/enhancement

Some licences have somewhat inconsistent names throughout this repo's packages, so I presume they could be merged so that each licence type has one `License:` value each.

I've for instance noticed at least 12 names used for for GPL-3.0 in `License` values:
```
GPL-3.0
GPL3
GPLv3
GPL-3
GPL-3.0 License
GPLv3 License
GPL-3 Licence
GPL-3 License
GNU General Public License v3
GNU General Public License v3 (GPLv3)
GNU General Public License v3.0
GNU General Public License v3.0 (GPLv3)
```
GPL-3.0 seems to be used in a large plurality of the packages, and would be the most obvious candidate to become the licence's synchronised `License:` name. But if anyone have other thoughts on the sync name, I'd be all ears.

A little over 1,000 packages seem affected, of which around 380 have those that are not `License: GPL-3.0`.

I presume the same situation applies to GPL-2.0, BSD-3, and to a smaller degree MIT.

### Proposed technical implementation details (optional)

Get a bot to run the following case-insensitive RegExes in the repo:
* (For GPL-3.0 if synced to "GPL-3.0") `^License: (GPL-3( ?Licen[sc]e)?|(GNU )?General Public Licen[sc]e[ -]v?3(\.0)?( ?\(GPLv3\))?|GPLv?3(\.0)?( ?Licen[sc]e)?|GPL-3\.0 ?Licen[sc]e)$` → `License: GPL-3.0`
* (For GPL-2.0 if synced to "GPL-2.0") `^License: (GPL-2( ?Licen[sc]e)?|(GNU )?General Public Licen[sc]e[ -]v?2(\.0)?( ?\(GPLv2\))?|GPLv?2(\.0)?( ?Licen[sc]e)?|GPL-2\.0 ?Licen[sc]e)$` → `License: GPL-2.0`
* I'd be able to calculate for BSD-3 on request.

Start by locating the package manifests containing License values and checking the proposed case-insensitive GPL-3.0 and GPL-2.0 patterns against them. Determine how a bot or bulk-edit process would safely update the affected packages, then verify that all intended variants are normalized without changing unrelated metadata.

Written by the indexing model from the issue text.