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>

templates/repo/upload.tmpl

@@ -0,0 +1,13 @@
+<div
+	class="ui dropzone"
+	id="dropzone"
+	data-upload-url="{{.UploadUrl}}"
+	data-remove-url="{{.UploadRemoveUrl}}"
+	data-accepts="{{.UploadAccepts}}"
+	data-max-file="{{.UploadMaxFiles}}"
+	data-max-size="{{.UploadMaxSize}}"
+	data-default-message="{{.i18n.Tr "dropzone.default_message"}}"
+	data-invalid-input-type="{{.i18n.Tr "dropzone.invalid_input_type"}}"
+	data-file-too-big="{{.i18n.Tr "dropzone.file_too_big"}}"
+	data-remove-file="{{.i18n.Tr "dropzone.remove_file"}}"
+></div>