Is your feature request related to a problem? Please describe.
We don't want to use the default ServiceAccount to run the solver-pod for HTTP01

Describe the solution you'd like
We'd like to configure the ServiceAccount to use, preferably by allowing that to be specified within the podTemplate-configuration in the solvers-stanza ( https://cert-manager.io/docs/configuration/acme/http01/#podtemplate )

Describe alternatives you've considered
We've tried to find a way to configure this to no avail.

Additional context
Add any other context about the feature request here.

Environment details (if applicable):

• Kubernetes version (e.g. v1.10.2): 1.14.10-gke.27
• Cloud-provider/provisioner (e.g. GKE, kops AWS, etc): GKE
• cert-manager version (e.g. v0.4.0): v0.9.1
• Install method (e.g. helm or static manifests): Static manifests

/kind feature