SNOW-878073 Refactor retry policy to support HTTP 503 & 429

[sfc-gh-dheyman]

Description

Please explain the changes you made here.

Checklist

• Code compiles correctly
• Run make fmt to fix inconsistent formats
• Run make lint to get lint errors and fix all of them
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary

[codecov]

Codecov Report

Merging #919 (0159c0f) into master (ce9ef59) will decrease coverage by 0.16%.
The diff coverage is 98.24%.

@@            Coverage Diff             @@
##           master     #919      +/-   ##
==========================================
- Coverage   83.26%   83.11%   -0.16%     
==========================================
  Files          49       49              
  Lines        9340     9327      -13     
==========================================
- Hits         7777     7752      -25     
- Misses       1563     1575      +12     

Files	Coverage Δ
auth.go	80.48% <100.00%> (+0.10%)	⬆️
authokta.go	78.42% <100.00%> (ø)
client.go	100.00% <100.00%> (ø)
connection.go	84.41% <ø> (ø)
dsn.go	87.57% <ø> (ø)
heartbeat.go	69.84% <100.00%> (ø)
restful.go	80.92% <100.00%> (-0.12%)	⬇️
telemetry.go	97.26% <100.00%> (ø)
util.go	98.26% <100.00%> (+0.09%)	⬆️
retry.go	93.65% <97.43%> (+4.81%)	⬆️

... and 1 file with indirect coverage changes

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