♻️ Simplify RUM assembly

[amortemousque]

Motivation

RUM assembly has a quite convoluted logic to handle the various contexts. More precisely:

• All context extends Context making us beleave they can contain any attribute ([x: string]: ContextValue) which is false.
• It's hard to follow the overridden logic of context with the combine
• It's hard to understand the service and version logic

Changes

• Only RumContext now extends Context
• Remove urlContext, viewContext, { action: { id: actionId } } from the combine and use simple assignment
• Remove convoluted viewContext service and version logic and use simple assignment

Testing

• Local
• Staging
• Unit
• End to end

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I have gone over the contributing documentation.

[BenoitZugmeyer]

💬 suggestion: ‏ we need to extend Context here just to work around the Index signature for type 'string' is missing in type ... error, but RumContext is never actually used with an index, except when using combine.

Maybe we could remove the extends here, and cast the object as RumContext & Context where RumContext is used with combine. WDYT?

I know this is a bit confusing, and there is a long standing TS issue related to that.

[BenoitZugmeyer]

🥜 nitpick: ‏maybe remove the view extra-level from those contexts