Run `onSendEvent` middleware hooks for `step.invoke()` payloads

[jpwilliams]

Summary

The onSendEvent.transformInput() middleware hook is used to intercept events being sent and change either the shape or number of events being sent. When invoking a function via step.invoke(), an internal inngest/function.invoked event is sent, though the onSendEvent.transformInput() hook is not currently run.

For middleware like @inngest/middleware-encryption, this poses a challenge, as it can no longer encrypt fields when using step.invoke() instead of step.sendEvent().

This PR ensures that the hook is also used for events being sent via step.invoke(), such that middleware can now appropriately affect the payloads.

Some notes on design decisions here:

• The onSendEvent hook will be run for each individual step.invoke(). This is the same functionality as calling step.sendEvent() multiple times. While the transformInput() hook supports batched payloads, this makes it difficult to determine which payloads have been affected if a user has omitted some from the returned array.
• Unlike step.sendEvent() or inngest.send(), we do not allow a developer to omit the event to be sent by step.invoke()

Checklist

• [x] Added a docs PR that references this PR
• [x] Added unit/integration tests
• [x] Added changesets if applicable

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 507a51a358881339e7d05a1221ac13b117f08a2b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ------- | ----- | | inngest | Patch |

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[inngest-release-bot]

A user has added the prerelease/inngest label, so this PR will be published to npm with the tag pr-503. It will be updated with the latest changes as you push commits to this PR.

You can install this prerelease version with:

npm install inngest@pr-503

The last release was built and published from 507a51a358881339e7d05a1221ac13b117f08a2b.