fix: Simplify github config

[diervo]

Details

Adds GIT_REPO as an env variable and as a config option.

Does this PR introduce a breaking change?

• Yes
• No

Removes the old PROJECT_CONFIG map in favor of a simplify definition of the repo.

[salesforce-best-lwc-internal]

Benchmark comparison

Base commit: 5cb6c76 | Target commit: 60db0f5

object_keys (simple-benchmarks)	base(5cb6c76)	target(60db0f5)	trend
stringify_parse	35.50 (± 0.25 ms)	35.00 (± 0.40 ms)	1.41% 👍
deep_merge	25.40 (± 1.40 ms)	27.80 (± 1.10 ms)	-9.45% 👎

simple-item (lwc-examples-prod)	base(5cb6c76)	target(60db0f5)	trend
create_and_render	54.50 (± 1.60 ms)	50.65 (± 0.45 ms)	7.06% 👍

simple-item (lwc-examples-compat)	base(5cb6c76)	target(60db0f5)	trend
create_and_render	87.75 (± 1.35 ms)	84.30 (± 1.00 ms)	3.93% 👍