Ai provider update (#5254)

* Modulize ai providers

* Updates logging and debugging

* Update prompt input and corrected usage logging and storage

* Response to first comments

* Error removal

* Add changeset

* Refactor to lib files

* Consolidate getProvider calls

* Moves provider validation

* Allow project level override

* Update skill file

Author: BoDonkey

.changeset/lovely-mangos-brush.md

@@ -0,0 +1,9 @@
+---
+"@apostrophecms/ai-helper": minor
+---
+
+- Refactored to use provider files
+- Added provider files for OpenAI, Anthropic, and Gemini
+- Updated README to reflect new options
+- Updated image variation modal to take a second prompt
+- Added a skill file for creating custom providers