feat: add support for separate runtime config in json & yaml formats

[meskill]

Summary:
Allow to specify separate runtime config as input in the json/yaml formats.

To test it out:

cargo run -- start ./examples/jsonplaceholder.yaml

At the same time it's still possible to define everything in the graphql file

Issue Reference(s):
Fixes #... (Replace "..." with the issue number)

Build & Testing:

• I ran cargo test successfully.
• I have run ./lint.sh --mode=fix to fix all linting issues raised by ./lint.sh --mode=check.

Checklist:

• I have added relevant unit & integration tests.
• I have updated the documentation accordingly.
• I have performed a self-review of my code.
• PR follows the naming convention of <type>(<optional scope>): <title>

[codecov]

Codecov Report

Attention: Patch coverage is 26.12613% with 82 lines in your changes missing coverage. Please review.

Project coverage is 86.39%. Comparing base (316254c) to head (0c5e54e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cli/tc/init.rs	0.00%	47 Missing ⚠️
src/core/config/config.rs	27.90%	31 Missing ⚠️
src/cli/generator/source.rs	75.00%	2 Missing ⚠️
src/core/config/source.rs	85.71%	1 Missing ⚠️
tailcall-typedefs/src/main.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3221      +/-   ##
==========================================
- Coverage   86.46%   86.39%   -0.08%     
==========================================
  Files         282      282              
  Lines       28705    28724      +19     
==========================================
- Hits        24820    24816       -4     
- Misses       3885     3908      +23     

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