[10.x] Feat: Add color_hex validation rule

[nikopeikrishvili]

This PR adds a hex color validation rule to check that an attribute is a valid HEX color.
There are a couple of rules for HEX color to be valid:

Standard 6-Digit Hex Codes:
Format: #RRGGBB
Each pair of characters (RR, GG, BB) represents the intensity of red, green, and blue colors, respectively.
Each pair is written in hexadecimal format, ranging from 00 to FF.
Example: #FF0000 represents pure red, with maximum intensity of red and no green or blue.

Short 3-Digit Hex Codes:
Format: #RGB
A shorthand version where each character represents red, green, and blue, but with less precision.
Each character is in hexadecimal, ranging from 0 to F.
Example: #F00 is equivalent to #FF0000, both representing pure red.

Error message in case of error:

[apih]

@nikopeikrishvili @taylorotwell Can this be extended to cover alpha channel? I have the same name of rule defined in my apps, and currently this built-in version will fail the input from my users, since the values will contain alpha channel as well.

Reference: https://developer.mozilla.org/en-US/docs/Web/CSS/hex-color

[ahinkle]

Hey @apih,

I had a similar case -- which this PR will eliminate my custom rule. I contributed alpha channel support which was recently merged:

#49069

[apih]

Hey @ahinkle, thanks for your PR. I noticed that your PR allowed 5 digits value to pass, which is not valid, so I opened a PR myself to fix that.

#49070

[ahinkle]

Hey thanks! Good catch.

[siarheipashkevich]

@nikopeikrishvili is it possible to set one of the formats for validation? For example I need to accept only:
Standard 6-Digit Hex Codes:
Format: #RRGGBB

[ahinkle]

@siarheipashkevich You may have to write a custom rule for that. Laravel validation doesn't generally accept PRs of argument exclusions.