[DOCS-10034] Update Browser SDK beforeSend callback function details

[rtrieu]

What does this PR do? What is the motivation?

Updates the description for the beforeSend callback function with more details

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[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/rtrieu/docs-10034-browser-logs-sdk-beforesend-update/logs/log_collection/javascript

[cswatt]

I'm afraid I've left some pretty annoying feedback here

[cswatt]

What does this function do with the context argument—why would a user set it, and what is the effect of setting it?

I'm guessing it's for if a user wanted to only apply the beforeSend function to a subset of logs that match a specific context. When they set context, the beforeSend function applies only to logs that match context. Whatever it is, we should explicitly state it.

[cswatt]

What does isAborted indicate? For handlingStack, what does "where" mean—a location? Also, we should probably specify data type. For example (and these are just my guesses at filling in missing information):

Suggested change

	| Value | Use Case |
	|-------|---------|
	| `isAborted` | For network log events. |
	| `handlingStack` | For network, console, and logger events - this value shows where the log event was handled, which is useful for micro-frontends. |
	| Value | Data Type | Meaning | Use Case |
	|-------|---------|
	| `isAborted` | Boolean | Whether the log event is aborted. | For network log events. |
	| `handlingStack` | String | Where the log event was handled, which is useful for micro-frontends. For example... <insert example values> | For network, console, and logger events. |

It doesn't need to be in this exact format