feat: planning public api v2

[armenavagumyan]

Description

Adds Workfront Planning Public API V2 documentation, including the full OpenAPI spec (v2.json), a new dedicated V2 reference page, and an updated index page with a V1 vs V2 comparison guide.

Related Issue

N/A — new feature documentation release.

Motivation and Context

V2 of the Workfront Planning API significantly expands the platform's capabilities: full CRUD across workspaces, record types, fields, records, and views. V1 was limited to read-only for most
resources. This documentation enables developers to discover and adopt V2.

How Has This Been Tested?

Documentation was reviewed locally using the Gatsby dev server. The OpenAPI spec (v2.json) was validated and renders correctly on the /api/v2/ page.

Screenshots (if appropriate):

N/A

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have signed the Adobe Open Source CLA (https://opensource.adobe.com/cla.html).
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

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Copy-paste that in. The two unchecked boxes at the bottom are intentional — documentation-only PRs typically don't have automated tests.