Upgraded to Gradle 7 and other dependencies

[mockitoguy]

• Bumped major version given that we're updating Gradle to next major
• Latest Gradle version 7
• Latest Gradle plugin publish version
• More current spock version that works with Gradle 7
• Gradle wrapper files

[mockitoguy]

@koral--, interested in joining the Shipkit team / getting GitHub permissions to merge PRs?

[koral--]

I already have the permissions.