Add support for persisted sessions

[oed]

This PR adds support for sessions that are persisted. These sessions are created and loaded using DIDSession.get(...). The sessions use the new @didtools/key-webcrypto did provider where keys are stored securely in the browser (outside of DOM). These keys along with the Cacao are persisted using IndexedDB.

Currently only browsers are supported. The .get function will throw an error if called in nodejs.

How Has This Been Tested?

One new unit test where added that uses fake-indexeddb and jsdom jest env.

Definition of Done

• [ ] Update documentation to point to this method primarily, since it's more secure

[oed]

@zachferland do you think a method like hasSessionFor(account) would serve that purpose?

[zachferland]

@oed yeah that works, hasSessionFor(account) and returns list with resources for each or hasSessionFor(account, authopts/resources) and returns bool, probably the second makes sense