[Feature]: Use GraphQL to query repository issues

[Malcolmnixon]

Problem Statement

The Octokit API to query repository issues should be replaced with GraphQL.

Proposed Solution

The GitHubRepoConnector calls client.Issue.GetAllForRepository(owner, repo, new RepositoryIssueRequest { State = ItemStateFilter.All }) to get all issues (in any state).

This should be replaced with a call to a new GitHubGraphQLClient.GetAllIssues method. The method should also hard-code querying for issues in all states and handle all paging. The new record types should be created in GitHubGraphQLTypes.cs

The tests should be written in a GitHubGraphQLClientGetAllIssuesTests.cs class.

This should also be the last use of Octokit in the project, and so it should be removed and any final cleanup performed.

Alternatives Considered

No response

Usage Examples

Benefits

Removal of last Octokit methods and types.

Priority

Medium - Would improve my workflow

Willingness to Contribute

Yes, I can submit a pull request

Additional Context

No response

Checklist

• I have searched existing issues to ensure this is not a duplicate
• I have provided a clear description of the feature
• I have explained why this feature would be useful