Check if remote branch exists before creating new one

[michalschott]

This should fix issue 433

My idea is to update logic so it:

• check if remote branch exists
• if so, do checkout and rebase against source branch
• if no, process as it is

So annoying to see controller spamming with

argocd-image-updater-5d5c9cf6f4-nhtph argocd-image-updater time="2022-12-12T16:14:40Z" level=error msg="Could not update application spec: could not push image-updater-jetstack/cert-manager-cainjector-v1.7.3-jetstack/cert-manager-controller-v1.7.3-jetstack/cert-manager-webhook-v1.7.3 to origin: `git push origin image-updater-jetstack/cert-manager-cainjector-v1.7.3-jetstack/cert-manager-controller-v1.7.3-jetstack/cert-manager-webhook-v1.7.3` failed exit status 1: Warning: Permanently added 'bitbucket.org' (RSA) to the list of known hosts.\r\nTo [redacted]\n ! [rejected]        image-updater-jetstack/cert-manager-cainjector-v1.7.3-jetstack/cert-manager-controller-v1.7.3-jetstack/cert-manager-webhook-v1.7.3 -> image-updater-jetstack/cert-manager-cainjector-v1.7.3-jetstack/cert-manager-controller-v1.7.3-jetstack/cert-manager-webhook-v1.7.3 (non-fast-forward)\nerror: failed to push some refs to '[redacted]'\nhint: Updates were rejected because the tip of your current branch is behind\nhint: its remote counterpart. Integrate the remote changes (e.g.\nhint: 'git pull ...') before pushing again.\nhint: See the 'Note about fast-forwards' in 'git push --help' for details." application=cert-manager

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