DependencyVerificationIntegTest.groovy

Generate checksum file for dependency verification
This commit introduces the generation of a dependency
verification metadata file from the CLI. If the user
calls `--write-verification-metadata`, then an XML
file is generated (`gradle/verification-metadata.xml`).

This file will contain the checksums for all artifacts
required by a build, which includes:

- plugin artifacts
- jars and other artifacts requested via a `configuration`
- secondary artifacts (javadocs, classifiers, ...)

It does NOT include metadata of those artifacts (pom files,
ivy files, Gradle Module metadata).

It isn't required to resolve any configuration to get this
behavior: the build will automatically process all resolvable
configurations and _try_ to resolve them automatically. All
artifacts resolved during this process are going to be automatically
downloaded (if not already). Then SHA-1 and SHA-512 checksums
are computed for all those artifacts.

The current format is an XML file planned to support more than
just artifacts: module metadata AND signature information is
planned.

See #11398