feat: added support for headers in config

[laststylebender14]

Summary:
Briefly describe the changes made in this PR.

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

Build & Testing:

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

Checklist:

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 79.71014% with 56 lines in your changes missing coverage. Please review.

Project coverage is 85.48%. Comparing base (e99c5eb) to head (8c2e130).

Files	Patch %	Lines
src/cli/generator/config.rs	76.29%	32 Missing :warning:
src/cli/generator/generator.rs	0.00%	20 Missing :warning:
src/core/resource_reader.rs	96.15%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2240 +/- ## ========================================== + Coverage 85.43% 85.48% +0.05% ========================================== Files 234 234 Lines 22232 22419 +187 ========================================== + Hits 18994 19165 +171 - Misses 3238 3254 +16 ```

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[github-actions[bot]]

Bencher

Report	Sat, June 22, 2024 at 08:44:26 UTC
Project	tailcall
Branch	2240/merge
Testbed	benchmarking-runner

Click to view all benchmark results

Benchmark	Latency	Latency Results nanoseconds (ns) | (Δ%)	Latency Upper Boundary nanoseconds (ns) | (%)
from_json_bench	✅ (view plot)	7,156,100.00 (+0.47%)	7,260,137.58 (98.57%)
group_by	✅ (view plot)	535.66 (-6.38%)	641.41 (83.51%)
input/args.missing	✅ (view plot)	25.61 (+6.43%)	26.83 (95.47%)
input/args.nested.existing	✅ (view plot)	54.47 (+13.83%)	62.44 (87.23%)
input/args.nested.missing	✅ (view plot)	39.28 (+3.16%)	40.39 (97.27%)
input/args.root	✅ (view plot)	49.82 (+12.70%)	59.35 (83.95%)
input/headers.existing	✅ (view plot)	32.70 (+3.31%)	33.76 (96.85%)
input/headers.missing	✅ (view plot)	32.33 (+5.20%)	33.59 (96.26%)
input/value.missing	✅ (view plot)	23.18 (-1.17%)	25.00 (92.71%)
input/value.nested.existing	✅ (view plot)	40.38 (-2.86%)	45.09 (89.57%)
input/value.nested.missing	✅ (view plot)	37.09 (+1.31%)	38.65 (95.96%)
input/value.root	✅ (view plot)	35.53 (-6.83%)	41.65 (85.31%)
input/vars.existing	✅ (view plot)	7.44 (-4.87%)	8.80 (84.63%)
input/vars.missing	✅ (view plot)	11.93 (+23.29%)	13.02 (91.67%)
test_batched_body	✅ (view plot)	2,667.90 (-99.37%)	1,948,952.00 (0.14%)
test_batched_body #2	✅ (view plot)	1,796,500.00 (+5.37%)	1,830,008.36 (98.17%)
test_data_loader	✅ (view plot)	466,420.00 (-0.62%)	486,301.65 (95.91%)
test_handle_request	✅ (view plot)	151,660.00 (-3.10%)	172,871.98 (87.73%)
test_http_execute_method	✅ (view plot)	17,864.00 (-2.02%)	19,306.35 (92.53%)
with_mustache_expressions	✅ (view plot)	1,195.00 (+2.51%)	1,228.68 (97.26%)
with_mustache_literal	✅ (view plot)	709.04 (-1.60%)	773.82 (91.63%)

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