fix: Move check for default PromptTemplates in PromptTemplate itself

[ZanSara]

Related Issues

• fixes n/a

Proposed Changes:

• Move check for default PromptTemplates in PromptTemplate itself to allow an API like PromptTemplate('summarization')

How did you test it?

local run

Notes for the reviewer

n/a

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added tests that demonstrate the correct behavior of the change
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 5098730429

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 63 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 39.607%

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Files with Coverage Reduction	New Missed Lines	%
nodes/prompt/prompt_template.py	20	88.76%
nodes/prompt/prompt_node.py	43	58.76%

Totals
Change from base Build 5093124690:	-0.01%
Covered Lines:	8872
Relevant Lines:	22400

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💛 - Coveralls

[vblagoje]

LGTM, we'll get another boost in confidence signal once we rebase all pending PRs on top of this one.