refactor: Add new GitHub issue templates

[shirasassoon]

This pull request updates and expands the GitHub issue templates for the project, improving clarity and introducing new templates for documentation feedback and Copilot agent tasks. The changes standardize naming conventions and add more structured options for users and contributors to provide feedback or request help.

New issue templates:

• Added a detailed documentation feedback template to collect structured input on documentation issues and improvements. (.github/ISSUE_TEMPLATE/4-documentation.yml)
• Introduced a Copilot assignment template for internal use, enabling structured task assignment to the GitHub Copilot agent. (.github/ISSUE_TEMPLATE/5-copilot.yml)

Improvements to existing templates:

• Standardized the naming of issue templates by capitalizing key words for consistency and clarity. (.github/ISSUE_TEMPLATE/1-bug.yml, .github/ISSUE_TEMPLATE/2-feature.yml, .github/ISSUE_TEMPLATE/3-question.yml) [1] [2] [3]