Ability to change the strength of safety_checker

[suzukimain]

What does this PR do?

Fixes #9003

"""
About safety_Level.
`int` or `float` or one of the following
'WEAK',
'MEDIUM',
'NOMAL',
'STRONG',
'MAX'.
"""

#To see the filter strength.
pipe.filter_level() # 0.0 (default)

#--------------
#If you want to change the intensity.
pipe.safety_checker_level("STRONG")
pipe.filter_level() # 1.0

#--------------
# If numbers are used
pipe.safety_checker_level(3.0)
pipe.filter_level() # 3.0

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[suzukimain]

However, I could not solve the following two problems by myself.

1. regarding the warning message when safety_checker is weakened, the message when safety_checker=None is passed is used as is.
   (I was going to put in a modified message, but I was worried, so I decided it was better not to change it and copied it as is.)

2. for the number to replace when a string such as 'NOMAL' is entered, I have set the following, but I am not sure if this is the best value.

"WEAK": -1.0
"MEDIUM": -0.5
"NOMAL": 0.0
"STRONG": 0.5
"MAX": 1.0

Please let me know if there are other problems.
thank you

[suzukimain]

Hello, @yiyixuxu
Is there any problem?
I hope to not have caused any inconvenience. thank you for your cooperation.