Add repo specific issue templates

[azeey]

Summary

(Related to gazebosim/gz-sim#1461)

Override the org level issue templates in order to make the issue templates more specific to this repo. This is currently just a copy of the files from https://github.com/ignitionrobotics/.github, but we are planning to remove the GUI/Rendering section from the issue templates there.

Note, I had to copy both files in ISSUE_TEMPLATES even though we only need to override bug_report.md because Github will not use the org level defaults if it finds any files in the repo's ISSUE_TEMPLATES directory.

Test it

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #393 (f8d63b0) into ign-gui6 (eac2fc2) will decrease coverage by 34.97%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##           ign-gui6     #393       +/-   ##
=============================================
- Coverage     65.52%   30.54%   -34.98%     
=============================================
  Files            39       41        +2     
  Lines          5157     1748     -3409     
=============================================
- Hits           3379      534     -2845     
+ Misses         1778     1214      -564     

Impacted Files	Coverage Δ
include/ignition/gui/Helpers.hh
src/Conversions.cc
include/ignition/gui/MainWindow.hh
src/ign.cc
src/plugins/world_stats/WorldStats.cc
src/plugins/shutdown_button/ShutdownButton.hh
src/plugins/teleop/Teleop.hh
src/plugins/scene3d/Scene3D.cc
src/Plugin.cc
src/plugins/marker_manager/MarkerManager.cc
... and 70 more

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