fix(GlLabel): Fix visibility of underline on hover and focus state

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Current	This MR

Note:	I have noticed that on the Figma font and underline color for the right side text portion is always #1F1F1F (gray-950). But currently, the right side text portion font color is changing based on the background color of the left side text portion. So, in my fix color of the underline also changing based on the font color as a default behavior.

In the issue told to fix the underline on hover but it's not working on also in focus state. So, I have fixed that also.

Reason for this bug: Underline colors by defaults take from the font color of the text. When the color of the text on the left side turns into white, the underline color becomes also white on for the right side text portion too and it becomes invisible. We have two separate classes in the <a>..</a> tag. One for the left side and another for the right side text portion. Because we are not specified which class to apply which style this problem is occurring.

My solution: My solution is to override the CSS color which is currently applying for the right side too. By adding @include gl-text-decoration-underline property for the right side (in gl-label-text-scoped class) we can solve the problem without changing the logic of getting font color according to the background.

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