Add support for PP2_SUBTYPE_SSL_GROUP

[maskit]

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[maskit]

[approve ci centos]

[maskit]

[approve ci centos]

[maskit]

[approve ci centos]

[Copilot]

Pull request overview

Adds end-to-end support for the PROXY Protocol v2 TLS sub-TLV PP2_SUBTYPE_SSL_GROUP so that ATS can parse it, expose it via ProxyProtocol, and log it as a first-class log field.

Changes:

• Add PP2_SUBTYPE_SSL_GROUP constant and ProxyProtocol::get_tlv_ssl_group() accessor.
• Add a new logging marshal function and register a new log field (proxy_protocol_tls_group / pptg).
• Extend the Proxy Protocol v2 parser unit test and update logging field documentation.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/proxy/logging/LogAccess.cc	Implements marshaling of the TLS group string from PROXY Protocol context for logging.
include/proxy/logging/LogAccess.h	Declares the new marshaling method for the logging subsystem.
src/proxy/logging/Log.cc	Registers the new log field proxy_protocol_tls_group with symbol pptg.
include/iocore/net/ProxyProtocol.h	Defines PP2_SUBTYPE_SSL_GROUP and declares the new accessor.
src/iocore/net/ProxyProtocol.cc	Implements get_tlv_ssl_group() via existing SSL sub-TLV parsing logic.
src/iocore/net/unit_tests/test_ProxyProtocol.cc	Updates v2 TLV test fixture lengths and validates parsing of the new SSL group subtype.
doc/admin-guide/logging/formatting.en.rst	Documents the new pptg logging field.