Twig prompt templates

Problem/Motivation

Some prompts are very strict (for example, asking AI to return a correct JSON). These prompt segments could be provided by aiprompt module by default.

Steps to reproduce

Proposed resolution

Default prompt templates could be saved under regular /templates/aiprompt directory and probably could also evaluate to twig with some potential added benefit of making prompts programmable with available variables.

User interface:
1) Prompt template selection.
2) Button "Load template".
3) Text area, where user can edit the prompt.
4) Tokens selection

Rendering:
1) It should token replace the template

Remaining tasks

User interface changes

API changes

Data model changes