[Cashtab] Show an extension-advertising toast to users on chrome/brave desktop who do not have the extension installed

Summary:
T3283

Been meaning to do this for awhile but wanted to get the extension onto the proper storage API first

the logic has already mostly been built in and on standby for like ... a year or more

Test Plan:
npm test

go to cashtab.io on chrome or brave without the extension installed, see the toast
go with it installed, no toast
firefox, no toast
mobile, no toast

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D18588