new component: Jinja2Builder

[masci]

Is your feature request related to a problem? Please describe.

The PromptBuilder component has proven useful in other use cases than just building prompts, but adding a PromptBuilder (say) after a generator, solves several use cases but feels like a hack.

Describe the solution you'd like

I would like to have a component that generically builds strings using Jinja2 templates, pretty much the same features as the PromptBuilder just with a different semantic so it doesn't look like a hack anymore

Describe alternatives you've considered

Using the PromptBuilder to not building prompts

Additional context

This new component shouldn't replace PromptBuilder that has a clear purpose in Haystack's pipelines. It should be a new thing.

[masci]

Superseded by #6936