FEATURE: Allow oneboxing private GitHub URLs (#27705)

This commit adds the ability to onebox private GitHub
commits, pull requests, issues, blobs, and actions using
a new `github_onebox_access_token` site setting. The token
must be set up in correctly to have access to the repos needed.

To do this successfully with the Oneboxer, we need to skip
redirects on the github.com host, otherwise we get a 404
on the URL before it is translated into a GitHub API URL
and has the appropriate headers added.

spec/lib/onebox/engine/github_commit_onebox_spec.rb

@@ -51,6 +51,19 @@ RSpec.describe Onebox::Engine::GithubCommitOnebox do
         expect(html).to include("2 deletions")
       end
     end
+
+    context "when github_onebox_access_token is configured" do
+      before { SiteSetting.github_onebox_access_token = "1234" }
+
+      it "sends it as part of the request" do
+        html
+        expect(WebMock).to have_requested(:get, @uri).with(
+          headers: {
+            "Authorization" => "Bearer #{SiteSetting.github_onebox_access_token}",
+          },
+        )
+      end
+    end
   end
 
   describe "PR with commit URL" do
@@ -58,12 +71,9 @@ RSpec.describe Onebox::Engine::GithubCommitOnebox do
       @link =
         "https://github.com/discourse/discourse/pull/4662/commit/803d023e2307309f8b776ab3b8b7e38ba91c0919"
       @uri =
-        "https://api.github.com/repos/discourse/discourse/commit/803d023e2307309f8b776ab3b8b7e38ba91c0919"
+        "https://api.github.com/repos/discourse/discourse/commits/803d023e2307309f8b776ab3b8b7e38ba91c0919"
 
-      stub_request(
-        :get,
-        "https://api.github.com/repos/discourse/discourse/commits/803d023e2307309f8b776ab3b8b7e38ba91c0919",
-      ).to_return(status: 200, body: onebox_response("githubcommit"))
+      stub_request(:get, @uri).to_return(status: 200, body: onebox_response("githubcommit"))
     end
 
     include_context "with engines"
@@ -107,5 +117,18 @@ RSpec.describe Onebox::Engine::GithubCommitOnebox do
         expect(html).to include("2 deletions")
       end
     end
+
+    context "when github_onebox_access_token is configured" do
+      before { SiteSetting.github_onebox_access_token = "1234" }
+
+      it "sends it as part of the request" do
+        html
+        expect(WebMock).to have_requested(:get, @uri).with(
+          headers: {
+            "Authorization" => "Bearer #{SiteSetting.github_onebox_access_token}",
+          },
+        )
+      end
+    end
   end
 end