Add caching to prevent unintentional rebuilds

[ghost]

See: #86 (comment)
Also related: #84

[olegstepura]

Sorry to ping, but is any work planned on this?

[eshtadc]

Nothing has been started to my knowledge but this is still a problem and should be addressed. Care to take a stab at a PR?

[olegstepura]

Not sure I know this addon codebase that well to be honest. Also issue description lacks details of what is expected to be done and why/how this would help. I came back here (with some hope :) following a link in our codebase answering why we cannot have CSS hot reload and service workers together.

[jrjohnson]

@olegstepura we've been happy using #84 (comment) to have both. I don't really want service worker running in development anyway so I've just added that to a .env file.

[eshtadc]

So if I read the PR comment linked above correctly, the inline strategy will cause the index.html file to be overwritten breaking hot reload. The suggestion is to only rewrite index.html when the strategy or contents of the registration script change to force a rewrite. Now that it's on my mind I'll do some research into a way to accomplish this. Suggestions welcome :)