[BEAM-4393]: Copy root repo's LICENSE & NOTICE into shadowJar

[boyuanzz]

r: @kennknowles
cc: @apilloud

[apilloud]

LGTM! I verified that this fixes BEAM-4393.

Only one question: should this go in jar instead of shadowJar?

[boyuanzz]

Hey @apilloud , my understanding so far is, we use shadowJar to rewrite Jar. How do you feel like? @lukecwik

[apilloud]

I believe we run the jar rule to build a jar with only our code, then we run the shadowJar rule to bundle that jar with third party code. This only needs to be in shadowJar, but that leaves our code in jar without a LICENSE file.

[kennknowles]

That seems like a problem. The shadowJar is the real thing and the "normal" jar is just an intermediate calculation.

[boyuanzz]

I didn't find any Jar{} closure so far in https://github.com/apache/beam/blob/master/build_rules.gradle, which means, we possibly use the default configuration. I'm not sure whether we need LICENSE in Jar.

[kennknowles]

Yea, OK. I didn't mean this PR is wrong. It seems this PR does put the LICENSE in the actual thing we want to ship to users. I guess the rest has to do with the release process.

[kennknowles]

Merging in the interest of moving things slightly better. If our current release process is mostly right, then this PR fixes it.