For image gen, move guidelines from being system instructions to being part of the prompt

[dkotter]

What?

Closes #496

For image generation, add matching guidelines as part of the prompt instead of system instructions

Why?

Turns out some image generation models (like OpenAI) don't support system instructions. This was wrong advice by me on the PR that implemented guideline support (I must have been testing with Google only).

This means that trying to generate images using OpenAI when you have guidelines in place won't work if those are set as system instructions.

How?

Instead of setting the guidelines as a system prompt, append those to the prompt

Use of AI Tools

None

Testing Instructions

1. Pull this PR down
2. Ensure you have Image Generation turned on
3. Configure OpenAI as your AI Connector
4. Install the Gutenberg plugin and turn on the guidelines experiment
5. Add Site and Images guidelines
6. Generate an image and ensure it works

Changelog Entry

Changed - For image generation, set guidelines as part of the prompt instead of system instructions.

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.16%. Comparing base (3ec6c5e) to head (8e782c5).
⚠️ Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
includes/Abilities/Image/Generate_Image.php	50.00%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #497      +/-   ##
=============================================
+ Coverage      69.15%   69.16%   +0.01%     
  Complexity       981      981              
=============================================
  Files             63       63              
  Lines           4649     4648       -1     
=============================================
  Hits            3215     3215              
+ Misses          1434     1433       -1     

Flag	Coverage Δ
unit	69.16% <50.00%> (+0.01%)	⬆️

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[gziolo]

Code changes look good 👍🏻

[dkotter]

This was merged into develop (see 9518a7c) but GitHub isn't reflecting that status here. Going to manually close this out and just assume it's a GitHub glitch