make all created repos findable by adding a Github topic in CD

[bertsky]

It would be very useful if all GT repos which (successfully) used this template could be easily identified as such on Github.

The best way to achieve this IMO would be to have the gtrepo workflow add a step which uses the Github API (and Github Action Token) to add the topic automatically.

For the concrete string I would propose ocr-d-gt.

The next best thing at the moment is a Github search for the strings in the generated Readme.

[bertsky]

BTW, the above Github search does not even cover GT repos like the ones from ULB Halle, probably because their readme has been edited or is from an earlier version of the template.

I could not find any documentation on an official way to track instances of a template. There are repeated feature requests for this, and some discussions on workarounds, esp. on how to synchronise the instances with changes from upstream. For the latter, there is even a Github Action. Maybe we should include this ASAP so at least from then on new repos will easily be synced.

[bertsky]

BTW, the above Github search does not even cover GT repos like the ones from ULB Halle, probably because their readme has been edited or is from an earlier version of the template.

In fact: this search seems to cover them all.