docs: update the required golang version in the contributing.md

[chlins]

This pull request updates the CONTRIBUTING.md file to provide more accurate and centralized information about Go version requirements and dependency management. Instead of specifying a fixed Go version, it now directs contributors to check the go.mod file for the required versions.

Updates to Go version information:

• Updated the Go version requirement to reference the go.mod file instead of specifying a fixed version (v1.15) in the list of development tools.
• Replaced the explicit mention of Go version 1.15 or greater with a reference to the go.mod file for dependency version requirements.

Description

Related Issue

Motivation and Context

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[gaius-qi]

LGTM