Make the PushOver API retry and expire configurable.

[jlrgraham]

Add support for setting the retry and expire elements in the PushOver API: https://pushover.net/api

[codecov-commenter]

Codecov Report

Merging #609 (1c81c0c) into main (45ba3b0) will increase coverage by 0.27%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #609      +/-   ##
==========================================
+ Coverage   37.19%   37.47%   +0.27%     
==========================================
  Files          80       80              
  Lines        3576     3592      +16     
==========================================
+ Hits         1330     1346      +16     
  Misses       2246     2246              

Flag	Coverage Δ
unittests	37.47% <100.00%> (+0.27%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mqttwarn/services/pushover.py	100.00% <100.00%> (ø)

:mega: We’re building smart automated test selection to slash your CI/CD build times. Learn more

[jpmens]

Merged, thank you!