Implement CSV import and conversion to contestants

app/views/contestants/convert_csv.html.slim

@@ -0,0 +1,40 @@
+= form_with model: @form, url: "/contests/#{@contest.id}/import/#{@csv_import.id}" do |form|
+
+  .row.mb-3
+    .col
+      .form-floating
+        = form.select :name_column, [[t("helpers.none"), -1]] + Array.new(@content[0].count) {|i| [t("helpers.field") + "_#{i}", i] }, {}, class: "form-select"
+        = form.label :name_column
+          = t("contestants.import.name_column")
+
+  .row.mb-3
+    .col
+      .form-floating
+        = form.select :email_column, [[t("helpers.none"), -1]] + Array.new(@content[0].count) {|i| [t("helpers.field") + "_#{i}", i] }, {}, class: "form-select"
+        = form.label :email_column
+          = t("contestants.import.email_column")
+
+  .row.g-3
+    .col
+      table.table.table-striped.table-hover
+        thead
+          tr
+            - @content[0].each_with_index do |_, i|
+              th scope="col"
+                = t("helpers.field") + "_#{i}"
+            th scope="col"
+              = t("contestants.import.import_column")
+        tbody
+          - @content.each_with_index do |row, i|
+            tr scope="row"
+              - row.each do |value|
+                td
+                  = value
+              td
+                .form-check.form-switch
+                  = form.check_box "row_#{i}".to_sym, class: "form-check-input", checked: true
+
+  .row.g-3
+    .col
+      = form.submit t("helpers.buttons.confirm"), class: "btn btn-primary"
+