Add a skeleton "http_profile" package

[brianquinlan]

• Creates a new experimental package:http_profile (final name TBD)
• Will eventually implement the non-SDK HTTP Client Profiling design (TL;DR will allow non-SDK HTTP clients to record profiling information in a HttpClientRequestProfile instance and have that information displayed in the DevTools Network tab)

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[natebosch]

[nit] Avoid phrases for getters. For booleans we often start the doc with "Whether".

Suggested change

	/// Determines whether HTTP profiling is enabled or not.
	/// Whether HTTP profiling is enabled for the current zone's [HttpClient].

[brianquinlan]

I'm not sure if we want to pull the zone concept in here - I think that this is actually per isolate. But I stared the sentence with "Whether".

[natebosch]

Can you expand the commit message (I usually edit the first PR comment then copy it to the message when I squash/merge) to include more details about how this class will be used by the SDK/DevTools?

What code will fill these fields in?

[brianquinlan]

Update the commit message.