refactor!: explicitly enable/disable new relic

Description

This MR allows the operators to explicitly enable/disable the NewRelic integration. If the integration was already turned on (i.e., setting account ID to a non-0 value), the integration cannot be turned off by setting it again to 0 -- due to API errors.

This MR introduces a new variable to explicitly turn on/off the integration, regardless of the account ID's value. This should be considered a breaking change as the default value for the new variable is False.

Supporting information

https://tasks.opencraft.com/browse/SE-6143

Testing instructions

Steps to test the changes:

1. Proofread the code
2. Check out for the staging DO cluster locally and turn off/on the integration again (and apply the changes in between)

Dependencies

NA

Screenshots

NA

Checklist

If any of the items below is not applicable, do not remove them, but put a check in it.

• All providers include the new feature/change
• All affected providers can provision new clusters
• Unit tests are added/updated
• Documentation is added/updated
• The TOOLS_CONTAINER_IMAGE_VERSION in ci_vars.yml is updated
• The grove-template repository is updated

Additional context

NA