docs: update the required golang version in contributing.md

[chlins]

This pull request updates the CONTRIBUTING.md file to improve clarity and ensure consistency regarding Go version requirements and dependency management. The changes replace hardcoded Go version references with instructions to check the go.mod file for the required versions.

Updates to Go version requirements and dependency management:

• Replaced the hardcoded Go version (v1.15) with a reference to the go.mod file for determining the required version in the tools section. (CONTRIBUTING.md, CONTRIBUTING.mdL242-R242)
• Updated the dependency management section to instruct contributors to check the go.mod file for required dependency versions, instead of specifying a minimum Go version directly. (CONTRIBUTING.md, CONTRIBUTING.mdL259-R259)

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.

[Liam-Zhao]

LGTM

[chlins]

Move to dragonflyoss/community#31.