feat: initialize debugger on first call

[andreiltd]

This enables using content debugger for scripts that don't target wasi/http. Depending on how StarlingMonkey has been configured, maybe_init_debugger can be a nop or perform actual debugger initialization. There is currently a triple line of defense to prevent accidental debugger initialization:

• StarlingMonkey build must be configured with ENABLE_JS_DEBUGGER=ON
• StarlingMonkey runtime arguments must include the --enable-script-debugging option
• The environment variable DEBUGGER_PORT must be defined

[vados-cosmonic]

Hey @andreiltd thanks for submitting this -- I'm going to leave the review to @tschneidereit since he knows the C++ side better (and the change looks fine to me!) but I wanted to ask if there should be some documentation changes that should go along with this?

Right now everything is kind of jammed into README.md but whether there or in a docs/debugging.md or something file, it might be nice to save the context you've put into the description, along with the fact that we can now debug in both instances?

[andreiltd]

Hey! Good point. I think we need to choose where the debugger documentation should live and link to it from other projects. I would prefer to have a chapter in StarlingMonkey mdbook if we decide to move forward with it: https://andreiltd.github.io/StarlingMonkey/

[tschneidereit]

LGTM! Agreed with Victor on documentation, but given that we don't really have documentation for JS debugging at all right now, I don't want to block landing this on documentation. So I'll land it now, and we should talk about docs in more detail separately.