Adds gh-pages support

[martintmk]

Details on the issue fix or feature implementation

Introduces support for Github Pages for Polly using DocFx.

Closes #1561
Contributes to #1091

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (2c5fc26) 83.99% compared to head (b0716db) 83.99%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1593   +/-   ##
=======================================
  Coverage   83.99%   83.99%           
=======================================
  Files         280      280           
  Lines        6548     6548           
  Branches     1020     1020           
=======================================
  Hits         5500     5500           
  Misses        839      839           
  Partials      209      209           

Flag	Coverage Δ
linux	83.99% <ø> (ø)
macos	?
windows	83.99% <ø> (ø)

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[martintmk]

Merging as docs are still wip and to improve what we have now.