Commit Message: orca: fix the delimiter of the native http parser
Additional Description:

This should also be cherry-pick to 1.32 to fix this problem.

The previous ORCA parser will use : as the delimiter of key/value pair in the native HTTP report. This is wrong
based on the design document. The correct delimiter should be =. This change fixes the delimiter to =.
See #6614 and related documents for more details.

https://docs.google.com/document/d/1NSnK3346BkBo1JUU3I9I5NYYnaJZQPt8_Z_XCBCI3uA/edit?tab=t.0

Native HTTP header encoding.  Similar to the JSON dictionary format, we will define Endpoint-Load-Metrics as having 
key=value format and use standard HTTP header encoding to either send the metrics as a sequence of HTTP headers or 
as a single header with [comma separated](https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2) key-value 
pairs. E.g.  endpoint-load-metrics: TEXT cpu=0.3,mem=0.8,foo_bytes=123.

Risk Level: n/a.
Testing: n/a.
Docs Changes: n/a.
Release Notes: added.

Request variables

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sha	d27eeef
pr	37724
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actor	@wbpcode
message	orca: fix the delimiter of the native http parser...
started	1734575975.054998
target-branch	main
trusted	false

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