[Cashtab] [extension address passing p3] Add storage permissions to extension and add address to extension storage

Summary:
T2550

Depends on D12315

Add active extension wallet address to extension storage API on wallet load

Test Plan:

cd web/cashtab
npm run extension

In brave browser, navigate to brave://extensions (or chrome/extensions in Chrome)
Click 'update' to update your local cashtab extension
Open your local Cashtab extension and pop it out to its own tab
Open the dev console
In the dev console, for the first run, storedAddress will be undefined, but you will see after this msg 'Address <yourAddress> saved to storage under key 'address''
Switch wallets
Note that it saves the new address to this key
Refresh the page
Note 'Active wallet address already in extension storage' msg in dev console

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12316