github/issue_template: rework issue templates with github forms

.github/ISSUE_TEMPLATE/5_feature_request.yml

@@ -0,0 +1,22 @@
+name: "Request a new Feature"
+description: "Create a request for a new feature"
+labels: ["meta:feature-request"]
+body:
+- type: textarea
+  attributes:
+      label: "Expected behavior of the wanted feature"
+      description: >
+          Before requesting a new feature make sure it hasn't been
+          [requested yet](https://github.com/mpv-player/mpv/labels/meta%3Afeature-request).
+  validations:
+      required: true
+- type: textarea
+  attributes:
+      label: "Alternative behavior of the wanted feature"
+- type: textarea
+  attributes:
+      label: "Log File"
+      description: >
+          Even if you think it's not necessary at first, it might help us later to find
+          possible issues. Make a log file made with `-v -v` or `--log-file=output.txt` and
+          attach it to the issue.