setup readthedoc preview github ci for doc preview before merge

[pindge]

Reason for this pull request

Multiple pull requests were raised to address syntax errors and typos, with previews syntax error caused rendering issue can be fixed before merging

Proposed changes

• setup readthedocs preview ci

• Closes enable readthedoc preview to reduce typo or syntax fix prs #1345

• Tests added / passed

• Fully documented, including docs/about/whats_new.rst for all changes

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📚 Documentation preview 📚: https://datacube-core--1344.org.readthedocs.build/en/1344/

[codecov]

Codecov Report

Base: 92.34% // Head: 92.34% // No change to project coverage 👍

Coverage data is based on head (a3eb677) compared to base (f31812e).
Patch has no changes to coverable lines.

❗ Current head a3eb677 differs from pull request most recent head 29f6984. Consider uploading reports for the commit 29f6984 to get more accurate results

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1344   +/-   ##
========================================
  Coverage    92.34%   92.34%           
========================================
  Files          127      127           
  Lines        13583    13583           
========================================
  Hits         12543    12543           
  Misses        1040     1040           

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