feature: allow users to implement custom data converters.

[rustatian]

Reason for This PR

ref: https://github.com/temporalio/sdk-php/issues/276

Description of Changes

• Allow users to create a plugin data-converter, like HTTP middleware, and build custom RR binary.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.] [Reviewer TODO: Verify that these criteria are met. Request changes if not]

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [x] The description of changes is clear and encompassing.
• [x] Any required documentation changes (code and docs) are included in this PR.
• [x] Any user-facing changes are mentioned in CHANGELOG.md.
• [x] All added/changed functionality is tested.

[codecov-commenter]

Codecov Report

Merging #316 (d357772) into master (001c8fd) will decrease coverage by 0.01%. The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master    #316      +/-   ##
=========================================
- Coverage    3.71%   3.69%   -0.02%     
=========================================
  Files          19      19              
  Lines        1644    1650       +6     
=========================================
  Hits           61      61              
- Misses       1581    1587       +6     
  Partials        2       2              

Impacted Files	Coverage Δ
plugin.go	0.00% <0.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.