Allow Backend Weight to be 0

[kfoozminus]

• Update parser/haproxy-templates
• Update docs

Fixes #1387

[codecov-io]

Codecov Report

Merging #1396 into master will increase coverage by 0.08%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #1396      +/-   ##
=========================================
+ Coverage    3.66%   3.74%   +0.08%     
=========================================
  Files          35      35              
  Lines       19061   18640     -421     
=========================================
  Hits          698     698              
+ Misses      18236   17815     -421     
  Partials      127     127

Impacted Files	Coverage Δ
pkg/haproxy/api/types.go	11.11% <ø> (ø)	⬆️
apis/voyager/v1beta1/annotations.go	29.79% <ø> (ø)	⬆️
pkg/ingress/parser.go	3.49% <0%> (-0.01%)	⬇️
apis/voyager/v1beta1/openapi_generated.go	0% <0%> (ø)	⬆️
pkg/ingress/controller.go	15.85% <0%> (+1.4%)	⬆️

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