Cannot change the user password - unclear error message

[milanmajchrak]

Describe the bug
This occurs when the user wants to change the password.
It is not clear why the user cannot change the password.
For instance (according to the validation policies which are set up in the BE: DSpace/DSpace#8254) the password must be at least 8 characters long, but if it less then 8 chars and the user want's to change the password. Only unclear message pops up: An error occurred while trying to change the password.

To Reproduce
Steps to reproduce the behavior:

1. Go to the user profile
2. Try to change password with less than 8 characters

Expected behavior
It would be nice to show the specific validation reason why the password validation has failed instead of default message. I suggest to show specific message from the error response.

Related work
#2378