feat(css): Add orange-300 && blue-400 utility mixins

What does this MR do?

Adds gl-text-orange-400 && gl-text-blue-400 mixins as those colors are used for severity icons coloring and are missing currenly

Related MR: gitlab!45671 (merged)

Does this MR meet the acceptance criteria?

Conformity

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• Added the ~"component:*" label(s) if applicable.

Security

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