chore: hardening soundness script

[Garfeild]

Motivation:

CONTRIBUTING.md describes that project provides way of basic validation of the changes by running scripts/soundness.sh.

Unfortunately, this script doesn't provide meaningful results and fails for multiple reasons:

• main branch contains large amount of code, which SwiftFormat tries to update to match rules;
• some DocC contains warnings, that result in failed check in the script due to returned exit code;
• one of the checks/scripts tries to build already removed package for Instruments.

Modifications:

• Correct link to Cluster.Node is added to documentation for Cluster.Endpoint, this fixes validate_docc.sh script
• validate_format.sh is updated to run SwiftFormat only against files, that are modified in the branch
• --lint option is passed to SwiftFormat to not modify files during validation run
• validate_instruments.sh is removed as step from soundness.sh and from the project
• Instruments directory is removed as it contains only leftovers
• CONTRIBUTING.md is updated with actual path to commits template.

Result:

• soundness.sh provides right feedback for your current working branch.