Refactor History/Visibility Archiver implementation

Now we have three implementations for the history archiver interface (filestore, s3 and gcp) and two implementations for the visibility archiver interface (filestore and s3). They all look quite similar and share lots of common utility functions.

We can move those common functions to the archiver package so that they can be reused. We can also consider abstract some common structure into a new component.

Also consider adding a context.Context parameter to the ValidateURI method.