CacheOverride Simplifications

[guybedford]

We could simplify the CacheOverride interface with the following steps:

1. Make the first string arg optional - replace new CacheOverride('override', { ... }) with just new CacheOverride({ ... })
2. Treat new CacheOverride('none') as just cacheOverride: null | undefined or otherwise
3. Treat new CacheOverride('pass') as just cacheOverride: 'pass' or even cache: 'no-store' per Support fetch cache option #1050
4. Support the CacheOverride being passed as an interface of options directly instead of having to have it explicitly constructed

With the above, we could then potentially deprecate the constructor in due course.