Remove weak and/or hardcoded user passwords from specs

What does this MR do and why?

Resolves Use random passwords in specs (#360030 - closed), and is leap forward towards unblocking Blocks weak passwords on sign up or password ch... (!86310 - merged).

Our specs use static passwords, many of them are weak. This makes it difficult to create changes which introduce password complexity constraints.

This MR updates instances where we set weak or hardcoded passwords to use randomly generated passwords.

All specs should be functionally equivalent. That is, no behaviour has changed, and things which made a test case pass/fail previously should still cause it to pass or fail.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #360030 (closed)