[nr-k8s-otel-collector] Allow using EU endpoint when populating license key from a secret

[dmd77]

Description

Currently, the endpoint for the otlphttp/newrelic exporter is being set via the "nrKubernetesOtel.endpoint" helper, which checks whether the license key has the "eu" prefix and returns the NA/EU endpoint accordingly.
This doesn't work when the license key is stored inside a secret, which is then referenced in the "customSecretName" and "customSecretLicenseKey" values.

Acceptance Criteria

It should be possible to use the EU endpoint for the otelhttp/newrelic exporter when providing the license key via secret.

Describe Alternatives

The most straightforward solution would be adding a new value that allows you to specify which endpoint you want to use which, when specified will take precedence over the "nrKubernetesOtel.endpoint" helper.

Dependencies

None, the helper is not part of the common library.

Additional context

None

Estimates

T-Shirt size: S

For Maintainers Only or Hero Triaging this bug

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