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/sw.ts

@@ -10,6 +10,8 @@ type Self = Window &
     sw: SWReplay;
   };
 
+// TODO: Fix this the next time the file is edited.
+// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
 if ((self as Self).registration) {
   const staticData = new Map();