cache.config -> cache.yaml

[bneradt]

cache.config needs to move to cache.yaml, with a supported migration
path for existing deployments. cache.yaml becomes the default format,
while cache.config remains available when explicitly selected.

This adds a shared cache parser and marshaller used by traffic_server
and traffic_ctl. The new traffic_ctl config convert cache command
converts legacy files to cache.yaml or writes the result to stdout.

This also addresses #7701 by giving cache.yaml ordered, first-match
semantics, so broader rules no longer compound actions after a specific
match. The legacy cache.config parser retains its additive behavior.

Fixes: #7701

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Pull request overview

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Comments suppressed due to low confidence (3)

doc/developer-guide/cache-architecture/architecture.en.rst:481

• This statement is too absolute: cache pinning is driven by the cache rule configuration selected by proxy.config.cache.control.filename. During migration, pinning can still be configured via legacy cache.config when explicitly selected, so the docs should not imply cache.yaml is the only option.

Objects can only be pinned via :file:`cache.yaml` and while
:ts:cv:`proxy.config.cache.permit.pinning` is set to non-zero (it is zero by

doc/developer-guide/cache-architecture/architecture.en.rst:105

• The sentence mixes plural subject with singular verb ("are derived" ... "is recomputed") and it reads as if only cache.yaml can drive cache layout. ATS can still be configured to use legacy cache.config via proxy.config.cache.control.filename, so this paragraph should refer to the cache rule configuration generally and fix the grammar.

This issue also appears on line 480 of the same file.

The layout and structure of the cache spans, the cache volumes, and the cache
stripes that compose them are derived entirely from :file:`storage.yaml` and
:file:`cache.yaml` and is recomputed from scratch when the
:program:`traffic_server` is started. Therefore, any change to those files can
(and almost always will) invalidate the existing cache in its entirety.

doc/developer-guide/cache-architecture/data-structures.en.rst:101

• CacheControlResult is used for both cache.yaml rules and legacy cache.config entries (depending on proxy.config.cache.control.filename). The description should avoid implying it only applies to cache.yaml.

   Holds the actions and match state from a rule in :file:`cache.yaml`.