Use Java 17 as default to compile and run Web3Signer code

[usmansaleem]

Use Java 17 as default to compile and run Web3Signer code. Web3Signer uses Besu's Metrics service as a dependency which is now compiled in Java 17 and cannot be used with Web3Signer when later is compiled using Java 11.

Tasks:

• Update gradle build file and update warning that Java 17 and upward can only be used for compilation
• Remove jdk11 docker image and distDocker logic in gradle build file
• consider updating signers library to build for Java 17 too (may not want to do this until Teku is Java 17 since they rely on it and may need security patches).
• Announce in Discord and Slack plans to Java 17 for next release.