Add S3 cache

[iNikem]

Enables remote Gradle cache on S3, closes #490

First, S3 bucket permissions should be rechecked based on https://github.com/burrunan/gradle-s3-build-cache#s3-bucket-permissions-for-cache-population. Cache should be readable for everybody, without credentials. In order to write to cache, we have to provide credentials. Plugin does require its own pair of env variables (not to mess with default configs locally). GHA populate them from secrets, which are available only on master branch. This is automatically guarantee that only nighty build on master can populate cache. And all other builds, including local on developers machines, can read that cache.

This is complimentary to GHA Gradle cache that we already have. Both will do their part to, hopefully, reduce our build times .

[anuraaga]

Who's key is this? Hope it's CNCF's.

[iNikem]

right now - Trask :) We are still waiting on open-telemetry/community#392

[trask]

yeah, we should get CNCF's soon, but wanted to unblock us in the short term

[trask]

Policy for the ACCESS_KEY_ID / SECRET_KEY:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "s3:PutObject"
            ],
            "Resource": [
                "arn:aws:s3:::otel-gradle-cache-temp/*"
            ]
        }
    ]
}

And public access is not blocked, so I think that means anyone should be able to GetObject?