SQSCANGHA-56 Support GitHub self-hosted runners without keytool

[antonioaversa]

Successful run here

This PR uses the keytool embedded in the JRE inside the scanner, instead of relying on the keytool command being installed on the environment running the action.

The PR also introduces QA tests checking the full SSL flow (previously QA only checked that the p12 file was in the right place).
The test is done via an nginx serving https port 4443 with a self-signed certificate (generated on the fly).
The nginx instance forwards to a local SQ instance on port 9000.

The PR merges into dev (which currently points to v4.0.0) since master should stay on v3.0.0 until December 9th.

[antonioaversa]

@Godin @henryju I have made updates to the PR, to fix the healthcheck of nginx, which was just waiting for 60 seconds and then moving on. I have now added a health endpoint on port 8080, which ensures that docker compose up waits for nginx to be in an operational state, before proceeding with the rest of the action.
The PR is ready, and you can proceed with the review.

[henryju]

Very nice, I like the use of nginx to test SSL, this is something I will likely reuse ;)

I think you can remove the generation of the client SSL certificate, but otherwise, LGTM!