ESLint parity with the Browsertrix repo (#288)

This copies the rules from the Browsertrix repo, and uses
[`suppress-eslint-errors`](https://www.npmjs.com/package/suppress-eslint-errors)
to suppose the violations. I'll take a pass at cleaning this up at some
point in the future, and let's do our best to address these in the
future as we come across them :)

This'll help ensure new code being added to this repo is held to the
same standard as code in Browsertrix's frontend.

src/item-info.ts

@@ -234,6 +234,8 @@ class ItemInfo extends LitElement {
   onCopy(event: Event, text: string | undefined) {
     event.preventDefault();
     event.stopPropagation();
+    // TODO: Fix this the next time the file is edited.
+    // eslint-disable-next-line @typescript-eslint/no-floating-promises
     if (text) navigator.clipboard.writeText(text);
     return false;
   }