feat: Add Copilot coding agent and content exclusion org endpoints

[AbhishekAg]

Implement support for two Copilot organization management endpoints under the CopilotService.

• Add ListCopilotCodingAgentRepositories for GET /orgs/{org}/copilot/coding-agent/permissions/repositories.
• Add GetCopilotOrganizationContentExclusionDetails for GET /orgs/{org}/copilot/content_exclusion.
• Add tests covering both endpoints, JSON round-trip tests for the new types, and regenerate accessors and iterators.

API docs:

• https://docs.github.com/rest/copilot/copilot-coding-agent-management#list-repositories-enabled-for-copilot-coding-agent-in-an-organization
• https://docs.github.com/rest/copilot/copilot-content-exclusion-management#get-copilot-content-exclusion-rules-for-an-organization

Fixes: #4175

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.20%. Comparing base (daaa203) to head (7dcd064).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4176      +/-   ##
==========================================
- Coverage   93.69%   93.20%   -0.49%     
==========================================
  Files         210      210              
  Lines       19706    24627    +4921     
==========================================
+ Hits        18463    22953    +4490     
- Misses       1047     1478     +431     
  Partials      196      196              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[gmlewis]

Thank you, @AbhishekAg!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @alexandear - @zyfy29 - @Not-Dhananjay-Mishra - @munlicode

[AbhishekAg]

The uncovered block at github/copilot.go:L233-L236 flagged by Codecov is the pre-existing json.Marshal error branch in CopilotSeatDetails.UnmarshalJSON.It's an unreachable branch: the input is a map[string]any that was just populated by json.Unmarshal, so it's guaranteed marshalable.

This PR's own additions are at 100% coverage (go test ./github/ -coverprofile shows no uncovered blocks in the new code).

@gmlewis Please override the Codecov check.
I am happy to open the small PR to clean-up the dead code.