add helm vars / fix extravars

for extraVars to work properly, e.g. by using

extraVars:

• name: POLICY_REPOSITORY_CLONE_URL value: "https://github.com/merlot-education/ssi-tsa-policies.git"

as values, the definition in deployment.yaml should not be indented.

also add possibly to configure NATS env vars, seems to be a new requirement (at least NATS_ADDR) as of commit dd353865