Add ability to generate new keypair for a specific user email (alias)

[martgil]

Description:

The FlowCrypt browser extension does offer a feature to generate another keys if they wish to.

However, it only generates another keypair for the current email address and does not offer user to generate it to another email address (email alias).

It would be ideal for it to have an option to show and let user to choose if it was to generate key for the email alias they have. For instance, the suggested feature would have been aided user who are experiencing issue in sending secure email using their email alias:

flowcrypt-browser/extension/chrome/elements/compose-modules/formatters/general-mail-formatter.ts

Line 45 in 7adc496

} else if (!(await GeneralMailFormatter.isSenderInKeyUserIds(view, signingKey.key))) {

[sosnovsky]

Great idea! Let's add dropdown with list of current user email aliases above passphrase section:

But it should be visible only for users who have email aliases.
When user has a single email - this dropdown should be hidden.