feat(develop): Allow to pass user_agent as browser context

[mydea]

Related to #13203

Today, the browser context is inferred in relay from event.request.headers['user-agent']. This is slightly weird in the context of a browser event, as the page is not really the request - we want to replace this with something more explicit.

In order to make this possible, we propose to allow client SDKs to send a partial browser context with only user-agent, and have relay infer the rest of the data from this, if it exists (instead of from event.request).

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[lforst]

sgtm. Before we merge this we should actually implement this in Relay.

[mydea]

After talking with @Dav1dde we will actually not do that, because it is hard for relay to partial-update contexts. Instead, relay can use the user-agent from the browser envelope request itself, which should already be here - which is great, because it means the SDK does not need to do/send anything 💪

[lforst]

After talking with @Dav1dde we will actually not do that, because it is hard for relay to partial-update contexts. Instead, relay can use the user-agent from the browser envelope request itself, which should already be here - which is great, because it means the SDK does not need to do/send anything 💪

Scary. In the case of tunneling this information is lost. "Hard for relay to partially update contexts" also seems a bit ridiculous.

[cleptric]

We actually need to figure out how this will be handled in Relay fist.

• If there is no browser context, Relay creates one
• How does the presence of a user_agent fit in in the current behavior
• How do we merge partial context