Temporary passwords for public non-anonymous protected shares (ie: files shared with an email recipient).

[StCyr]

This PR implements #31005

With this change, passwords protecting public non-anonymous shares become temporary: They have an expiration time and a background job changes them to some random undisclosed value when their expiration time is passed.

To request a new temporary password, recipients use a new "request password" button that is added to protected public non-anonymous shares' authentication page. This button serves the same functionality as the "request password" button implemented by Talk (ie: To identify the person requesting the password), except that, here, the person identifies herself by proving she knows the email address with which the file is shared with (ie: she types her email address, and if it matches the email address with which the file is shared the person is considered "identified" and a new temporary password is sent to that email address). Of course, identification via a Talk session takes precedence when the share has its "video verification" attribute checked.

I'm waiting for your reviews and welcome your comments which I hope will be constructive

Cyrille

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UPDATE 20220217:

1. The existing protected public non-anonymous shares are not impacted by this change (they don't have a password_expiration_time, so the expiration background job doesn't consider them)
2. The temporary passwords are valid for 1 day.

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UPDATE 20220223:
I've created a new branch: https://github.com/nextcloud/server/tree/enhancement/31005/temporary-passwords-v2

Compared to this branch, this new branch brings the following:

1. password_expiration_time is now checked during password check. This also makes the expiration background job not necessary anymore;
2. Temporary passwords validity period is now configurable via a system value