feat: add debug capabilities

[Convly]

What does it do?

• adds a dependency to the npm debug package (54kB) and supports-color (10kB)
• introduce debug logs for critical parts of the SDK lifecycle (initialization, validation, http client, auth, content-type managers)

Also

• fix repo configuration around lint, tests and pre-commit scripts

Why is it needed?

Better traceability and maintainability of the codebase.

Easier issue management/reproduction with finegrained logs

How to test it?

DEBUG=* node main.js # debug everything
DEBUG=sdk:auth:* node main.js # debug every auth module
DEBUG=sdj:ct:* node main.js # debug content type managers
DEBUG=*,-sdk:validators:* node main.js # debug everything except validators

TODO

• add documentation