Enable custom domains for Github Issue provider

[radhajain]

Description

Enables users to pass custom domains for the github issue provider

Checklist

• [X] The base branch of this PR is dev, rather than main
• [X] The relevant docs, if any, have been updated or created

Testing

Able to set the domain name to the user's choice, e.g.:

{
  "name": "issue",
  "params": {
    "repos": [
      {
        "owner": "continuedev",
        "repo": "continue"
      }
    ],
    "githubToken": "ghp_xxx",
    "domain": "github.acme-inc.com"
  }
}