🐛 [RUM-8428] Make developer extension compatible with lazy loaded recorder module

[sethfowler-datadog]

Motivation

Lazy loading the recorder extension involves dynamically import()ing the module from a separate JS chunk, stored at a separate URL. The developer extension doesn’t know about this URL, so it doesn’t redirect it to the version served by yarn dev appropriately, breaking local development.

Changes

This PR fixes the problem by making two changes:

1. Updating our webpack configuration to remove the context hash from the recorder chunk filename in local development, so that it gets hosted at a consistent localhost URL. (Nothing has changed in production builds.)
2. Updating the developer extension to redirect fetches of the recorder chunk to the appropriate localhost URL when local development is enabled.

Testing

• Local
• Staging
• Unit
• End to end

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I have gone over the contributing documentation.