Generate ad-hoc signed JAR in JarResultBuildStepTest

[gastaldi]

In #40001 we're using the dependency plugin to download an already signed JAR to run the JarResultBuildStepTest. It would be nice if we could create one on the fly if possible (with Shrinkwrap?) and then sign it with some randomly generated keys.

Originally posted by @galderz in #40001 (comment)

[quarkus-bot]

/cc @Sanne (core), @aloubyansky (core), @geoand (core), @gsmet (core), @radcortez (core), @stuartwdouglas (core)

[DShivansh]

Hey @gastaldi
I was thinking of picking this issue so far I have figured out how to make a jar using shrinkwarp but I am not sure how to sign the jar programmatically do you have any suggestions on this.

[DShivansh]

Hi @galderz
I saw your comment -> #40001 (comment)
I was just wondering whether we can use bouncycastle as I could not find any other way to generate certificate on the fly.

[galderz]

@DShivansh That's probably fine, just add it as a test dependency.

[DShivansh]

@galderz @gastaldi can you please review the pr