[Component] Lead space search

[oliviaflory]

Updated v2 design specs

Updates to the component in v2:

• For v2, we will deprecate the image background variant for lead space search. This is to ensure that the centered lead space heading and subheading can maintain proper contrast across breakpoints.
• Removed title and subheading discrepancy. Now there is only one heading for the component.
• New highlight span can be added to the heading (no where else). Highlight can apply to a word or words anywhere in the heading.
• New Dotcom color token to handle highlight across lead space components: $heading-highlight.
• Updated spacing values to bring in line with content block/section. Margin at top and bottom.
• No more 90% container width for text. Text width is now more in-line with content block (instead of 90% of container)
• Use Carbon core's search set to the large sizing.
• Search is now flush with the columns (no overhang)