THREESCALE-8916: Make strong passwords mandatory

[jlledom]

What this PR does / why we need it:

Currently, a provider can enforce strong password for the developer portal, and weak passwords are accepted by default. About admin portal, there's no option to enable strong passwords, weak passwords are always accepted.

I think both situations make no sense. I don't think it's acceptable to allow users decide whether they enforce strong passwords or not, as long as strong passwords are possible, that should be the default. And same thing about admin portal.

In this PR, I remove any option to accept weak passwords in both admin or developer portals. Existing passwords will continue to work, but new passwords will be enforced to be strong. Also, I increased the minimal number of characters to 16.

This affects multiple screens, but also API endpoints, this is the complete list:

• All scenarios with a password
  • Admin portal
    • UI
      • User invitation signup form
      • Personal details
      • Edit user
      • Forgot password
    • API
      • POST /master/api/providers.xml
      • POST /admin/api/users.xml
      • PUT /admin/api/users/{id}.xml
  • Developer portal
    • UI
      • New buyer signup form
      • Existing buyer user invitation signup form
      • Personal details
      • Edit user
      • Forgot password
    • API
      • POST /admin/api/signup.xml
      • POST /admin/api/accounts/{id}/users.xml
      • PUT /admin/api/accounts/{id}/users/{id}.xml

Besides, while doing this, I found a few UI errors that I told Claude to fix. This are the affected screens:

• Admin portal
  • User invitation signup form
    • JS validation:
      • Before: min 6 characters
      • Now: Same restrictions as in backend
    • Error messages formatting
      • "\n" was literally printed instead of a new line.
  • Personal Details
    • Password input in clear text
  • Edit user
    • Password inputs visible for users without password (e.g. OAuth)
  • Create new buyer
    • Password input in clear text
  • Forgot password
    • Pass JS Validation: Sames as above

Another thing I noticed is strong passwords, even when enabled, were not being enforced for users not created by a human. For instance, the default admin user created when a buyer is created was always accepting weak passwords no matter the setting. I also fixed this.

Which issue(s) this PR fixes

https://issues.redhat.com/browse/THREESCALE-8916

Verification steps

You can go through any (ideally all) screens above an try to set a weak password. Also tests should pass.