Refactor: replace campaign custom post type with page

[jonwaldstein]

Resolves GIVE-2352

Description

We have decided to replace our initial campaign page custom post type with a general WordPress page. This will ensure wider coverage compatibility with the WordPress ecosystem in terms of front facing themes, plugins, and page builders.

With this new direction a few UX updates have been made including:

1. Campaigns now start off in active state, but the landing page is in draft.
2. Migrated campaigns will not create a page by default and instead will have a "Create campaign page button"
3. If an existing campaign page gets trashed, campaigns will have a "Create campaign page button"
4. All campaign blocks will be available on WordPress pages with a campaign selector

Affects

• New campaigns
• Form migrations to campaigns
• Campaign blocks

Visuals

Testing Instructions

ZIP: https://github.com/impress-org/givewp/actions/runs/14068715829

• Migrating existing forms to campaigns still works, can update campaign details and can create a campaign page
• New campaigns are active, can edit campaign with default blocks, status is in draft until published
• Campaign landing page can be publicly viewed in various WP themes and page builders
• Campaign block works as expected with ability to create a campaign page when one is not found for campaign
• Campaign grid works as expected and campaigns are only clickable when they have a landing page
• When a campaign page is trashed/deleted, the campaign will show a "create campaign page" button to create a new one.
• Campaign blocks can be used on any page

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed