Add cert-manager docs

[kfoozminus]

• cert-manger get-started
• http01 challenge
• dns01 challenge
  • aws-route53
  • azure-dns
  • google-dns
  • multiple provider together
• Add images

[codecov-io]

Codecov Report

Merging #1417 into master will increase coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #1417      +/-   ##
=========================================
+ Coverage    3.68%   3.88%   +0.19%     
=========================================
  Files          35      35              
  Lines       19055   19716     +661     
=========================================
+ Hits          702     765      +63     
- Misses      18224   18821     +597     
- Partials      129     130       +1

Impacted Files	Coverage Δ
pkg/ingress/controller.go	17.52% <0%> (-0.46%)	⬇️
pkg/ingress/nodeport.go	0% <0%> (ø)	⬆️
pkg/ingress/hostport.go	0% <0%> (ø)	⬆️
pkg/ingress/internal.go	0% <0%> (ø)	⬆️
pkg/ingress/loadbalancer.go	0% <0%> (ø)	⬆️
pkg/ingress/parser.go	4.45% <0%> (+0.96%)	⬆️
apis/voyager/v1beta1/annotations.go	31.41% <0%> (+1.78%)	⬆️
pkg/haproxy/api/types.go	14.58% <0%> (+3.47%)	⬆️

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[tamalsaha]

• Add all the yamls to https://github.com/appscode/voyager/tree/master/docs/examples/certmanager folder

[tamalsaha]

Does Voyager automatically mount this ssl cert?

[kfoozminus]

Cert-manager updates the tls-secret mentioned in Ingress.