feat: add scripts to retrieve repositories with and without Copilot custom instructions

[joshjohanning]

This pull request adds new scripts and documentation to help identify repositories with or without Copilot custom instruction files in a GitHub organization. The main changes are the introduction of two bash scripts for this purpose, along with updates to the README.md to describe their usage.

Copilot instruction detection scripts:

• Added get-repositories-with-copilot-instructions.sh to list repositories containing either repository-wide (.github/copilot-instructions.md) or path-specific (.github/instructions/) Copilot instruction files, including a formatted output option.
• Added get-repositories-without-copilot-instructions.sh to list repositories lacking both types of Copilot instruction files.

Documentation updates:

• Updated gh-cli/README.md to provide descriptions and usage instructions for the new Copilot instruction detection scripts.

[Copilot]

Pull request overview

Adds two gh-cli helper scripts to report which organization repositories do or do not contain Copilot custom instruction files, and documents them in the gh-cli script catalog.

Changes:

• Add get-repositories-with-copilot-instructions.sh to list repositories containing .github/copilot-instructions.md and/or .github/instructions/
• Add get-repositories-without-copilot-instructions.sh to list repositories missing both instruction locations
• Update gh-cli/README.md with usage docs for the new scripts

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
gh-cli/get-repositories-with-copilot-instructions.sh	New GraphQL-based detector script (includes tabular TSV output)
gh-cli/get-repositories-without-copilot-instructions.sh	New GraphQL-based detector script (outputs repositories missing instruction files)
gh-cli/README.md	Adds documentation entries for the two new scripts

Comments suppressed due to low confidence (1)

gh-cli/get-repositories-with-copilot-instructions.sh:7

• These scripts use the API to list organization repositories and read repository contents, but they don’t document the required gh auth scopes/permissions (for example, needing access to private repositories in the org). Add a short note near the top indicating the expected authentication/scopes (and/or an example gh auth refresh command) so failures are easier to diagnose.

# Get repositories that have Copilot custom instruction files
# Checks for:
#   - .github/copilot-instructions.md (repository-wide custom instructions)
#   - .github/instructions/ directory (path-specific custom instructions)
#