Attachments: Add extension support, allow all types for releases (#12465)

* Attachments: Add extension support, allow all types for releases

- Add support for file extensions, matching the `accept` attribute of `<input type="file">`
- Add support for type wildcard mime types, e.g. `image/*`
- Create repository.release.ALLOWED_TYPES setting (default unrestricted)
- Change default for attachment.ALLOWED_TYPES to a list of extensions
- Split out POST /attachments into two endpoints for issue/pr and
  releases to prevent circumvention of allowed types check

Fixes: https://github.com/go-gitea/gitea/pull/10172
Fixes: https://github.com/go-gitea/gitea/issues/7266
Fixes: https://github.com/go-gitea/gitea/pull/12460
Ref: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/file#Unique_file_type_specifiers

* rename function

* extract GET routes out of RepoMustNotBeArchived

Co-authored-by: Lauris BH <lauris@nix.lv>

integrations/attachment_test.go

@@ -43,7 +43,7 @@ func createAttachment(t *testing.T, session *TestSession, repoURL, filename stri
 
 	csrf := GetCSRF(t, session, repoURL)
 
-	req := NewRequestWithBody(t, "POST", "/attachments", body)
+	req := NewRequestWithBody(t, "POST", repoURL+"/issues/attachments", body)
 	req.Header.Add("X-Csrf-Token", csrf)
 	req.Header.Add("Content-Type", writer.FormDataContentType())
 	resp := session.MakeRequest(t, req, expectedStatus)