Add sshKnownHosts support

[mbaldessari]

Now you can add the following to your values-secrets-.yaml file:

bootstrap_secrets:
  - name: private-repo
    targetNamespaces:
      - openshift-operators
    labels:
      argocd.argoproj.io/secret-type: repository
    fields:
      - name: type
        value: git
      - name: url
        value: git@github.com:mbaldessari/mcg-private.git
      - name: sshPrivateKey
        value: |
          -----BEGIN OPENSSH PRIVATE KEY-----
          ...
          -----END OPENSSH PRIVATE KEY-----
      - name: sshKnownHosts
        value: |
          foo.bar ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl

And deploy the pattern via ./pattern.sh make TOKEN_SECRET=private-repo TOKEN_NAMESPACE=openshift-operators install

Verify that Argo's configmap has our added sshknownhosts:

oc get cm -n vp-gitops argocd-ssh-known-hosts-cm -o yaml |grep foo.bar
foo.bar ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl

Closes: #839

[openshift-ci]

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