Update doc for MutableException

[pbludov]

https://checkstyle.org/config_design.html#MutableException

Add example for each existing config to show what code is ok and what code cause violation.
Good example is https://checkstyle.org/config_naming.html#AbstractClassName
Look at referenced commits of #5832, to see what and how should be changed in code.

Please play with module/check by means of https://checkstyle.org/cmdline.html to understand how it works.

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PLEASE READ https://github.com/checkstyle/checkstyle/wiki/Good-practice-on-how-to-update-examples

[ShubhraSuman]

I am on it.

[ShubhraSuman]

Do I need to write example for both properties or one is fine? Since both of them have same default values.

name description type default value

• format Specify pattern for exception class names. Pattern "^.*Exception$|^.*Error$|^.*Throwable$"
• extendedClassNameFormat. Specify pattern for extended class names Pattern "^.*Exception$|^.*Error$|^.*Throwable$"

[romani]

For both, and both should have custom values (not defaults)

[arinmodi]

@pbludov, I made a PR on this, can you please review that ?