feat(app): tag User-Agent with concrete receiver class name (#1150)

[tmchow]

Summary

Closes #1150.

The Slack team wants to see which receivers bolt-js apps are actually running so they can prioritize missing features based on real usage. Today the only tag the WebClient emits for a bolt app is @slack/bolt/<version>, so every receiver is indistinguishable from every other.

This registers a second addAppMetadata entry whose name includes the concrete receiver class (for example @slack/bolt-HTTPReceiver, @slack/bolt-SocketModeReceiver, @slack/bolt-AwsLambdaReceiver, or the class name of a user-supplied custom receiver). It is registered from the App constructor after this.socketMode is resolved but before new WebClient(...) is constructed, because WebClient snapshots getUserAgent() into its axios headers at construction time. The existing module-load-time addAppMetadata({ name: '@slack/bolt', version }) entry is left in place so the base package tag remains, which keeps existing telemetry consumers working.

addAppMetadata writes to a module-global map inside @slack/web-api, so a Node process that constructs multiple App instances with different receiver types will accumulate both entries in every subsequent WebClient's User-Agent. In single-App processes (the common case) the tag is exact; in multi-App processes the tag set is a superset of the receiver types that App has constructed, which over-attributes but does not under-attribute receiver usage. A tighter per-App scoping would require piping a custom User-Agent through clientOptions and bypassing the module-global metadata path, which is a larger design decision; happy to take that route if you prefer.

Verified with npm run build (clean), npm run lint (Biome, 136 files, no fixes applied), and npm run test:unit (465 tests, including a new receiver-type app metadata case in test/unit/App/basic.spec.ts that asserts addAppMetadata is called with a name ending in -FakeReceiver when an app is built with a custom receiver).

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[salesforce-cla]

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[tmchow]

I signed the CLA