Add/Update git templates from old-master

[postscript-dev]

The Exiv2 GitHub templates were lost during the transition from the master branch to main branch.

[postscript-dev]

Do we still need the text at the beginning? e.g.,

--- name: Feature request about: Suggest an idea for this project title: '' labels: FeatureRequest assignees: '' --- 

[codecov]

Codecov Report

Merging #1988 (3a1a9db) into main (76a9377) will increase coverage by 0.02%.
The diff coverage is n/a.

@@ Coverage Diff @@ ## main #1988 +/- ## ========================================== + Coverage 61.26% 61.29% +0.02%  ========================================== Files 96 96 Lines 19105 19110 +5 Branches 9756 9760 +4 ========================================== + Hits 11705 11713 +8  + Misses 5079 5076 -3  Partials 2321 2321 

Impacted Files	Coverage Δ
src/actions.cpp	61.29% <0.00%> (+0.15%)	⬆️
src/exiv2.cpp	58.18% <0.00%> (+0.33%)	⬆️

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[kmilos]

Do we still need the text at the beginning?

It think so, especially to set up the tags and assignees... However, it seems issue templates moved now to a more sophisticated YAML scheme, but this one is still good enough for the time being.