Drop support for Python v3.6 and EPEL 8 from Apprise

[caronc]

Description:

Related issue (if applicable): n/a

Python v3.6 has been cumbersome to maintain. A lot of patch files to maintain with Rocky Linux 8, plus unit testing has all kinds of edge cases that just simply do not work. Logic in the Apprise code has several spots where it reads acts in such a way "IF Python v3.6, then do this instead to remain compatible...."

This PR ends the support for Python 3.6 completely and with that EPEL 8 management.

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• No lint errors (use flake8)
• 100% test coverage

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.28%. Comparing base (6733953) to head (ec814ab).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #1155    +/-   ##
========================================
  Coverage   99.28%   99.28%            
========================================
  Files         142      142            
  Lines       18440    18440            
  Branches     3763     3544   -219     
========================================
  Hits        18309    18309            
  Misses        121      121            
  Partials       10       10            

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