use liquid templates

[aleksei-okatiev]

This PR allows to store prompts as a liquid template.
Liquid has iterators and allows to store if else logic inside the prompt.

An example of usage for refine test case prompt:

"Goal of the test:
'''
{{goal}}
'''

Out of scope:
'''
{{out_of_scope}}
'''

Additional requirements:
'''
{{additional_requirements}}
'''

Feature Description:
'''
{{test_features}}
'''

Original Gherkin Test Case to refine:
'''
{{test_case_content}}
'''

{% if compared_screenshots_message %}
Difference between the last two screenshots:
'''
{{compared_screenshots_message}}
'''
{% endif %}

{% if html_diff_message %}
Changes in HTML after the last test case step:

{{html_diff_message}}
{% endif %}

{% if passed_parents %}
Chain of previous versions of the test case:
{% for test_case in passed_parents %}
'''
{{ test_case }}
'''
{% endfor %}
{% endif %}

{% if passed_relatives %}
Other test cases already executed, please avoid generation of the same test cases:
{% for test_case in passed_relatives %}
'''
{{ test_case }}
'''
{% endfor %}
{% endif %}