Add issue templates for bugs, feature requests and documentation improvements

[gsheni]

• Added issue templates for creating bugs, feature requests and documentation improvements
• Added Slack link to issue creation

[codecov]

Codecov Report

Merging #1834 (d204d14) into main (9cc0306) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1834   +/-   ##
=======================================
  Coverage   98.79%   98.79%           
=======================================
  Files         142      142           
  Lines       15850    15850           
=======================================
  Hits        15659    15659           
  Misses        191      191           

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