POC - Implements Conjur OSS database as postgresql Helm subchart

[diverdane]

This branch implements the Conjur OSS backend database as a
Helm subchart. The Helm subchart imports from the bitnami/postgreql chart.

Needs some work to:

• Autogenerate a Postgresql password by default
• Set the database.url value based on that password
• Use checksum/config annotations with hashes to selectively
  recreate pods in the Conjur-OSS cluster but not the Postgresql
  cluster.

To deploy Conjur with a Postgresql database, run:

DATA_KEY="$(docker run --rm cyberark/conjur data-key generate)"
CONJUR_NAMESPACE=conjur-with-subchart
PG_PASSWORD=0mbkLSg9ah
PG_NAMESPACE="$CONJUR_NAMESPACE"

kubectl create namespace "${CONJUR_NAMESPACE}"
helm install \
   -n "${CONJUR_NAMESPACE}" \
   --set dataKey="${DATA_KEY}" \
   --set rbac.create=false \
   --set database.url="postgres://postgres:${PG_PASSWORD}@conjur-oss-postgresql.${PG_NAMESPACE}.svc.cluster.local:5432/postgres" \
   --set postgresql.postgresqlPassword="${PG_PASSWORD}" \
   conjur-oss .

What does this PR do?

• What's changed? Why were these changes made?
• How should the reviewer approach this PR, especially if manual tests are required?
• Are there relevant screenshots you can add to the PR description?

What ticket does this PR close?

Resolves #86

Checklists

Change log

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