feat: add allowEmptyCase option to no-fallthrough rule

[amareshsm]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[x] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Refs: #15703

What changes did you make? (Give an overview)

Change to the existing rule no-fallthrough.

Added an option to allow empty cases in the switch case.

Is there anything you'd like reviewers to focus on?

What rule do you want to change?

no-fallthrough

Does this change cause the rule to produce more or fewer warnings?
yes, if allowEmptyCase option is enabled will not show any error for empty cases.
How will the change be implemented? (New option, new default behavior, etc.)?
new option
Please provide some example code that this change will affect:

var foo = 2;
var a = function (){
    console.log('sample function');
}
switch(foo){
    case 1:
    /*
    Put a message here 
    */
    case 2: a();
}

What does the rule currently do for this code?

Throws error for the empty rule.
Error:

Expected a 'break' statement before 'case'. ([no-fallthrough](https://eslint.org/docs/rules/no-fallthrough)) 

What will the rule do after it's changed?

/* eslint no-fallthrough: ["error", { "allowEmptyCase": true }] */

If we set allowEmptyCase to true, won't show errors for empty cases regardless of blank lines and comments inside.

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[mdjermanovic]

Thanks for the PR!

Can you also update the documentation for this rule: docs/src/rules/no-fallthrough.md

[amareshsm]

Thanks for the PR!

Can you also update the documentation for this rule: docs/src/rules/no-fallthrough.md

updated the documentation.

[mdjermanovic]

@amareshsm are you still working on this? Please feel free to let us know if you need any help or more information. It would be nice to finish this, and I think it's close.

[amareshsm]

@amareshsm are you still working on this? Please feel free to let us know if you need any help or more information. It would be nice to finish this, and I think it's close.

Quite Held up this week. I will look into this soon. I will let you know if I need any help.

[nzakas]

@amareshsm just checking back to see if you are still working on this?

[amareshsm]

Changes done. PR is ready for review

[mdjermanovic]

LGTM, thanks!

I'll leave this open for a few days in case someone else wants to review it before merging.