Fixes #838 - docs: Move item types under reference documentation

[cmaneu]

Description

This pull request reorganizes the documentation by moving the item type documentation from the "How To" section to a new "Reference" section. It also updates navigation and links to reflect this new structure, making it easier for users to find detailed reference material.

Linked Issue (REQUIRED)

#838

[Copilot]

Pull request overview

This pull request reorganizes the MkDocs documentation structure by introducing a dedicated Reference section and relocating “Item Types” and “Code Reference” content under it, while updating affected internal links and adding a changelog fragment for the docs change.

Changes:

• Updated mkdocs.yml navigation to add a new “Reference” section and move “Item Types” + “Code Reference” under it.
• Added docs/reference/index.md and docs/reference/code_reference.md to establish the new Reference landing page and API docs entry point.
• Updated docs/reference/item_types.md links to correctly point back to the “How To” parameterization page.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
mkdocs.yml	Adds “Reference” to site navigation and relocates related pages under it.
docs/reference/item_types.md	Fixes relative links to parameterization content now that the page lives under reference/.
docs/reference/index.md	Introduces a landing page for the new Reference section with section TOC markers.
docs/reference/code_reference.md	Adds the mkdocstrings entry page for fabric_cicd under Reference.
.changes/unreleased/docs-20260506-134300.yaml	Adds a Changie docs fragment documenting the reorganization.