feat: support multiple resolvers on fields

[meskill]

Summary:
Briefly describe the changes made in this PR.

Issue Reference(s):
Fixes #3120

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 94.89051% with 21 lines in your changes missing coverage. Please review.

Project coverage is 86.73%. Comparing base (d053a88) to head (8c5a7b4).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/core/config/resolver.rs	67.50%	13 Missing ⚠️
src/core/config/transformer/subgraph.rs	72.72%	3 Missing ⚠️
src/core/merge_right.rs	97.27%	3 Missing ⚠️
src/cli/tc/init.rs	0.00%	1 Missing ⚠️
src/core/ir/eval.rs	98.46%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3124      +/-   ##
==========================================
+ Coverage   86.69%   86.73%   +0.04%     
==========================================
  Files         275      276       +1     
  Lines       27319    27493     +174     
==========================================
+ Hits        23683    23845     +162     
- Misses       3636     3648      +12     

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[tusharmath]

@meskill Thanks! This is a great PR. We need to update the docs for each directive here — https://tailcall.run/docs/tailcall-dsl-graphql-custom-directives/

[meskill]

@meskill Thanks! This is a great PR. We need to update the docs for each directive here — https://tailcall.run/docs/tailcall-dsl-graphql-custom-directives/

added documentation here tailcallhq/tailcallhq.github.io#560