Start CSV importer feature

app/views/contestants/import.html.slim

@@ -0,0 +1,19 @@
+= form_with(model: @csv_import, url: contest_import_path(@contest), html: { novalidate: true }) do |form|
+  .row.g-3
+    .col
+      .mb-3
+        .form-floating
+          = form.file_field :file, class: "form-control", accept: ".csv, text/csv"
+          = form.label :file
+
+  .row.g-3
+    .col
+      .mb-3
+        .form-floating
+          = form.select :separator, @csv_import.options_for_separator, {}, class: "form-select"
+          = form.label :separator
+
+  .row.g-3
+    .col
+      .mb-3
+        = form.submit t("helpers.buttons.import"), class: "btn btn-primary"