[Docs] pillar documentation update

Description of Issue

As noted in closed ticket https://github.com/saltstack/salt/issues/55106 the documentation on pillars and pillar caching is confusing and needs an overhaul, likely the new working group can audit these docs and help with consistency and reader flow.

Setup

Possible docs to review (there may be more or less):

• pillar.items https://docs.saltstack.com/en/latest/ref/modules/all/salt.modules.pillar.html#salt.modules.pillar.items

• pillar.raw https://docs.saltstack.com/en/latest/ref/modules/all/salt.modules.pillar.html#salt.modules.pillar.raw

• pillar caching https://docs.saltstack.com/en/latest/ref/configuration/master.html#pillar-cache-options

Steps to Reproduce Issue

(Include debug logs if possible and relevant.)

Versions Report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)

Start by reviewing the pillar.items and pillar.raw documentation pages and the pillar-cache-options section linked in the issue, then compare their explanations for consistency and reader flow. Done means the pillar and pillar-caching documentation has been audited and revised to remove confusing guidance; check the closed issue #55106 for context.