Add Inspector V2 development notices and PR template

[olaservo]

Summary

Add Inspector V2 development notices and create pull request template to help contributors understand version targeting and contribution scope.

Motivation and Context

Inspector V2 is under active development to address architectural improvements (monolithic components, OAuth flows, configuration management, and UX enhancements). Contributors need clear guidance on:

• What types of contributions are appropriate for V1 vs V2
• How to participate in V2 development
• Where V2 planning discussions are happening

Without this information, contributors may:

• Submit large architectural PRs that would be better suited for V2
• Report issues that are already planned to be addressed in V2
• Miss opportunities to participate in V2 development

How Has This Been Tested?

TBD

Breaking Changes

No breaking changes.

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

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally (N/A - documentation only)
• I have added appropriate error handling (N/A - documentation only)
• I have added or updated documentation as needed

[cliffhall]

LGTM! 👍