fix: decouple devMode and postgres egress

[noahpb]

Description

Updates the internal keycloak helm chart to be more explicit about using an external postgres database connection.
Notable changes are:

• Configures egress rule and keycloak env vars for postgres based on postgresql being populated
• Defaults postgresql.username, postgresql.password, postgresql.database, and postgresql.host to an empty string
• Adds option to enable debug logging via debugMode: true
• Adds a fail case when devMode is true and postgresql has values defined
• Adds fail cases when users do not supply required values for postgresql when devMode is false

Related Issue

Fixes #489

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide followed

[noahpb]

In the codecentric helm chart for keycloak, the postgres values are used to configure the postgres dependency. I considered renaming postgres to something like database or externalPostgres to reflect that we're no longer using the postgres subchart, but opted not to as this would be a breaking change.