Fix workhorse secret

Summary

Workhorse secret must be a base64 encoded string of 32-byte data.

# Gitlab-workhorse secret
generate_secret_if_needed "gitlab-gitlab-workhorse-secret" --from-literal="shared_secret"=$(gen_random 'a-zA-Z0-9' 32 | base64)

Currently, we do not base64 encode the generated secret, causing the error:

Success criteria

• Workhorse secret is fixed