Use GraphQL API to get issue template

[skanehira]

👔 Overview

Currently use REST API to get issue template from https://api.github.com/repos/:owner/:repo/git/trees/:branch but it's not better because we must filter files to get templates.

gh.vim/autoload/gh/github/repos.vim

Line 22 in 0b695e6

\ 'url': printf('https://api.github.com/repos/%s/%s/git/trees/%s', a:owner, a:repo, a:branch),

I found GraohQL API that can get issue template only.
Use this API we can improve get issue template to better.

https://docs.github.com/ja/graphql/reference/objects#issuetemplate

request

query {
  repositoryOwner(login: "skanehira") {
    repository(name: "gh.vim") {
     	issueTemplates {
        about
        body
        name
        title
      } 
    }
  }
}

response

{
  "data": {
    "repositoryOwner": {
      "repository": {
        "issueTemplates": [
          {
            "about": "Bug report",
            "body": "## 🐛 Summary\n<!--\nThanks your report.\nPlease write summary of bug.\n-->\n\n## 💔 Enviroment\n- Vim/Neovim Version:\n- OS: \n\n## 👀 Steps\n<!--\nPlease write how reproduce the bug.\n-->\n1. Do action\n2. Do another action\n3. Wrong Behavior !!\n\n## 🆗 Expected\n\n\n## 🚑 Actual\n\n\n",
            "name": "Bug report",
            "title": null
          },
          {
            "about": "Request",
            "body": "## 👔 Overview\n<!--\nThanks your request.\nPlease write summary of request.\n-->\n\n## 👖 How to achieve\n<!--\nHow to achieve the feature\n-->\n\n## 🧦 Steps\n<!--\nHow to use this feature\n-->\n\n1. Do action\n2. Do another action\n3. Wrong Behavior !!\n\n",
            "name": "Request",
            "title": null
          }
        ]
      }
    }
  }
}

👖 How to achieve

1. Replace REST API to GrpahQL API to get issue templates

🧦 Steps

No current operations and changes