Commit Message:
This PR picks up the work done in #25804.

1. It adds a receive_before_connect filter state which can be read by TCP_PROXY and if set TCP_PROXY will not disable downstream reads until the upstream connection is established. This can hence be used by filters before TCP_PROXY to set the filter state in initializeReadFilterCallbacks, and then StopIteration in onNewConnection and onData, until they have read the required amount of data before upstream connection establishment.
2. Based on feedback in #25804 , this PR adds a flow control to prevent early_data_buffer from overflowing, by disabling downstream reads on early data until the upstream connection establishment is finished.
3. Adds integration and unit tests to cover the newly added functionality.

Additional Description:
Risk Level: Low
Testing: Added integration and unit tests
Docs Changes: Done
Release Notes:
Platform Specific Features:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional API Considerations:]

Request variables

Key	Value
ref	23f512a
sha	5c171de
pr	36581
base-sha	93d05d5
actor	@akshita31
message	Add filter state receive_before_connect to tcp_proxy...
started	1728937114.584562
target-branch	main
trusted	false

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