docs: update contributor policy, add contributing section, remove old…

[madvart]

existing - Daft_CONTRIBUTING.md.pdf existing-Contributing.pdf

new - subpage -Development Guide.pdf new - Contributing to Daft.pdf new - CONTRIBUTING.md - Grip.pdf

Changes Made

1. Divided CONTRIBUTING.md by moving details on development to a sub page (https://docs.daft.ai/en/stable/contributing/development)
2. Added Contributor Policy on CONTRIBUTING.md

Related Issues

Checklist

• [ ] Documented in API Docs (if applicable)
• [ ] Documented in User Guide (if applicable)
• [ ] If adding a new documentation page, doc is added to docs/mkdocs.yml navigation
• [ X] Documentation builds and is formatted properly (tag @/ccmao1130 for docs review)