feat: Add back hardcoded default templates

[silvanocerza]

Proposed Changes:

Add the hardcoded PromptTemplate remove with PR #4879.

How did you test it?

Add a new test that verifies the expected legacy template is returned when using legacy template names.

Notes for the reviewer

There's more information in the comment at the top of legacy_default_templates.py.

[TuanaCelik]

JFYI, the PR merged by @ZanSara renames prompt_text to prompt and removes name in PromptTemplate.

[silvanocerza]

@TuanaCelik yep, I noticed. I'm fixing it right now.

[coveralls]

Pull Request Test Coverage Report for Build 5059281109

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 44 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 39.549%

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Files with Coverage Reduction	New Missed Lines	%
nodes/prompt/prompt_node.py	44	59.34%

Totals
Change from base Build 5059192256:	0.04%
Covered Lines:	8855
Relevant Lines:	22390

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💛 - Coveralls

[ZanSara]

Ok, I see the value of these, but my concerns with this approach is: do we want to keep these local PromptTemplates forever, or not?

I see there's no deprecation schedule or hint they will eventually be deprecated. I'm ok with keeping them, but if so, let's not call them "legacy" or similar names: we should find a stable place for them that makes sense. Also, I'd rather distinguish them strongly from the ones in the hub: question-answering and deepset/question-answering are too similar to trigger such different behavior in PromptTemplate. Right now, basically one works as expected (the first) and the other does not.

If we don't want to support output parsers in the hub, then we either go head-in with this decision and deprecate these prompts, or backtrack and rethink the integration. And to be honest I believe output parsers could be supported in the hub (I'm volunteering for this task if necessary) so, if we need them so badly, we should consider this option too.

In short, I see this solution here as valid only if it's a patch to ease the transition. Let's clarify what's our stand on this.

[ZanSara]

Let's clarify what we want the API to look like before moving forward

[ZanSara]

Ok after some discussion, let's add a deprecation notice to these templates. It should be enough for now.

[ZanSara]

This could be enough to clarify the situation imho.

[ZanSara]

Overall this is probably good like this. We'll consider if deprecating the default templates or not later, depending on usage too. No need to block the hotfix for that 🙂