Establish password restriction rules

[KFie]

It is currently possible to register with a password consisting of a single character only. To better resemble real-world shops, we should establish basic password restriction rules.

Suggestion: password should consist of at least 8 characters, one capital letter and one number.

Requirements

• Implement password restriction rules as described above
• If a customer tries to sign up violating these rules, they see error messaging

Storefront display

Display password restriction rules in small font below the password input field (in line with #192)

Wording

"At least 8 characters, one capital letter, one number"