Add rateLimit to BackendTrafficPolicy

[arkodg]

Relates to #1821 & #2006

[codecov]

Codecov Report

Merging #2060 (488960e) into main (a00d289) will decrease coverage by 0.12%.
Report is 1 commits behind head on main.
The diff coverage is 62.41%.

@@            Coverage Diff             @@
##             main    #2060      +/-   ##
==========================================
- Coverage   65.17%   65.06%   -0.12%     
==========================================
  Files          99       99              
  Lines       14410    14536     +126     
==========================================
+ Hits         9392     9458      +66     
- Misses       4437     4491      +54     
- Partials      581      587       +6     

Files	Coverage Δ
internal/gatewayapi/helpers.go	83.90% <100.00%> (+0.12%)	⬆️
internal/gatewayapi/translator.go	98.50% <100.00%> (ø)
internal/status/backendtrafficpolicy.go	0.00% <0.00%> (ø)
internal/gatewayapi/backendtrafficpolicy.go	64.53% <64.70%> (-4.14%)	⬇️

... and 3 files with indirect coverage changes

[zhaohuabing]

What happens if both a "RateLimitFilter" and the "RateLimit" of a "BackendTrafficPolicy" attach the same route? Will "RateLimitFilter" API be deprecated?

[arkodg]

What happens if both a "RateLimitFilter" and the "RateLimit" of a "BackendTrafficPolicy" attach the same route? Will we deprecate "RateLimitFilter"?

@zhaohuabing the plan is to remove RateLimitFilter (& AuthenticationFilter) before we release v0.6