Add alerts section to Canary CRD schema

[stefanprodan]

Fix: #793

[BarrieShieh]

hi, i think also need some definitions like username channel in AlertProvider too. https://github.com/fluxcd/flagger/blob/main/charts/flagger/crds/crd.yaml#L1077-L1150

[stefanprodan]

@BarrieShieh good catch! Thank you

[codecov-io]

Codecov Report

Merging #794 (52cec59) into main (4f54901) will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #794      +/-   ##
==========================================
+ Coverage   56.53%   56.61%   +0.07%     
==========================================
  Files          67       67              
  Lines        5391     5403      +12     
==========================================
+ Hits         3048     3059      +11     
- Misses       1881     1882       +1     
  Partials      462      462              

Impacted Files	Coverage Δ
pkg/canary/deployment_controller.go	64.63% <0.00%> (+1.29%)	⬆️

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