rename api key component to copy_to_clipboard

does what it says on the tin, and is also consistent with prior art:
https://components.publishing.service.gov.uk/component-guide/copy_to_clipboard

app/assets/stylesheets/components/copy-to-clipboard.scss

@@ -1,4 +1,4 @@
-.api-key {
+.copy-to-clipboard {
 
   position: relative;
   padding-bottom: 38px;  // height of button

app/assets/stylesheets/main.scss

@@ -50,7 +50,7 @@ $path: '/static/images/';
 @import 'components/file-upload';
 @import 'components/browse-list';
 @import 'components/email-message';
-@import 'components/api-key';
+@import 'components/copy-to-clipboard';
 @import 'components/vendor/previous-next-navigation';
 @import 'components/radios';
 @import 'components/checkboxes';