clean up @sentry/node submodule exports

[isaacs]

Description

Clean up the submodule exports of the @sentry/node module. It has a lot of these, mostly for legacy uses that are no longer relevant.

• ❌ @sentry/node/init Initialize the SDK from environment variables. Deprecate.
• ❌@sentry/node/preload Preload OTel instrumentation without init (init later in code). Deprecate.
• @sentry/node/import Calls Module.register('@opentelemetry/instrumentation/hook.mjs'). Keep, consider deprecating in the future, once Orchestrion instrumentations are ready to take over. Note: a case could be made to deprecate this in v11, with guidance to tell users to set up their own preload/instrument.js file.
• @sentry/node/loader Older form of @sentry/node/import, exported loader-hook style. Keep, consider deprecation in the future, once Orchestrion instrumentations ready to take over. Note: a case could be made to deprecate this in v11, with guidance to tell users to set up their own preload/instrument.js file.
• ✅ @sentry/node/auto-diagnostic-channels Add new entry point for experimental Orchestrion codemods. When these instrumentations are ready to take over, this should replace the @sentry/node/import and the older explicit verbose name should be deprecated.

cc: @nicohrubec

[linear-code]

JS-2761