Flatten OPA Helm values

[MattPrit]

Changes:

• Flatten structure of values.yaml for the OPA Helm chart. This means that chart users will configure things as, for example, opa.orgData.enabled rather than opa.opa.orgData.enabled. This brings things in line with the examples in docs/how-tos/deploy-with-helm.md.
• Revert opa.name and opa.fullname in charts/opa/templates/_helpers.tpl to the defaults created by helm create. This changes opa.name from opa-opa to opa and opa.fullname from release-name-opa-opa to release-name-opa.
• Fix what I think are typos in docs/how-tos/deploy-with-helm.md and docs/how-tos/verify-json-web-token.md