Enable logging by default [.NET]

Update logs behavior to follow the same opt-in model as `enableMetrics`:

* Users are considered opted-in when:
* They call the equivalent of `Sentry.logger.*`, or
* They explicitly enable a logging integration.
* Change default: set enable logs to `true`.
* Audit all logging integrations to ensure:
* No logs are emitted unless the integration is explicitly enabled.
* Update documentation:
* Explain new default behavior of `enableLogs`.
* Clarify requirement to explicitly enable logging integrations.