[newrelic-logging] Metrics host magic in `_helpers.tpl` relies on plain value secret to choose EU over US about helm-charts

[workato-integration]

https://new-relic.atlassian.net/browse/NR-281467

[TBeijen]

Luckily it is possible to override the endpoint. I now have this in my nri-bundle values:

nri-bundle:
  newrelic-logging:
    enabled: true
    # See:
    # - https://github.com/newrelic/helm-charts/blob/master/charts/newrelic-logging/values.yaml
    # - https://github.com/newrelic/helm-charts/issues/1399
    endpoint: https://log-api.eu.newrelic.com/log/v1

Admitted, this is not great DX. Probably initially only licence-key was supported and parsing for 'eu' was added. Then later, using an external existing secret was added, and things became complex and broke.

Parsing the licence key for a string imo has some downsides:

• No licence key in chart values, nothing to parse (this issue)
• Requires plain-text access to something that is a secret
• API key would best be opaque. Now NR will need to adhere to this format for times to come (can be a conscious choice though)

I would suggest adding something like region: us to the global settings, with the ability to set to 'eu', and using that for any conditional logic.