Address 3180: Rule file-header should have an option to allow // comments

[rrogowski]

PR checklist

• Addresses an existing issue: fixes Rule file-header should have an option to allow // comments #3180
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Config

{
  "rules": {
    "file-header": [true, "Good header", "", "allow-multiline"]
  }
}

Before

// **********************************
~nil [missing file header]
// Good header
// **********************************

After

// **********************************
// Good header
// **********************************

// No lint error for missing file header

CHANGELOG.md entry:

[new-rule-option] allow-single-line-comments for file-header rule

[JoshuaKGoldberg]

Implementation details LGTM, just waiting on the options object.

[rrogowski]

@adidahiya @JoshuaKGoldberg ready for second review.

[adidahiya]

allow-single-line-comments

[rrogowski]

@adidahiya Thanks for your comments. They have been addressed. Ready for another pass.

addressed