Cleanup branch name in PR Generators

[Aym3nTN]

Summary

In PR generators, I noticed that when a branch name contains special characters or is too long to be used in a resource name (by using {{branch}}), the applicationset controller fails to create the resource throwing the below exception.

argocd-applicationset-controller-647f5948d6-bq7sn time="2022-05-20T08:58:18Z" level=error msg="failed to unchanged Application" action=unchanged app=nginx-github-feat/pr_special+character-2 appSet=test-app-set-github error="Application.argoproj.io \"nginx-github-feat/pr_special+character-2\" is invalid: metadata.name: Invalid value: \"nginx-github-feat/pr_special+character-2\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')"

Motivation

In order to follow the DNS label standard as defined in RFC 1123, manifests' name metadata should not exceed 63 and must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character.

Docs: https://kubernetes.io/docs/concepts/overview/working-with-objects/names/#dns-label-names

Proposal

For that I suggest limiting and cleaning the 'branch' name to contain only 50 characters to give room to append/suffix-ing it with 13 more characters.