feat: Action filtering for webhook apps

[benjackwhite]

Problem

See https://github.com/PostHog/posthog/issues/21721 and https://github.com/PostHog/product-internal/issues/599

Needs https://github.com/PostHog/posthog/pull/22253

We want to replace the existing action webhooks with something a little more fit-for-purpose. To do this we need to:

1. Support filtering plugins by actions as a config option on the plugin
2. Allow webhook plugins to take care of templating the event into valid webhook content (e.g. for a slack webhook)

This PR attempts to solve problem 1

Changes

• [x] Refactors the ActionMatcher into the hub to be used by both webhook firing and composeWebhook processing
• [x] Moves reloading and pubsub into the ActionManager class as it feels more part of it.
• [x] Filters composeWebhoook plugins by the relevant action matcher if necessary
• [x] Adds option to the (legacy) UI behind a flag
• [x] Add tests for filtering logic
• [x] Ensure actions can not be deleted if they have connected plugins

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Follow up

• Create issue about the experiments/utils.py TODO

Does this work well for both Cloud and self-hosted?

How did you test this code?

[github-actions[bot]]

Size Change: +50 B (0%)

Total Size: 1.03 MB

ℹ️ View Unchanged

Filename	Size	Change
frontend/dist/toolbar.js	1.03 MB	+50 B (0%)

_{compressed-size-action}

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