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%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 76a9377...3a1a9db. Read the comment docs.

[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.