[EuiBadge] Prevent color opacity

[thompsongl]

Per discussion in #2850, now that we've opened up EuiColorPicker to opacity we may want to do more than give console warnings for invalid color input. For instance, 8-digit hex values are still renderable by EuiBadge but are not desirable and can cause contrast failures.

#2804 is related for validation reasons

Solutions:

• Set alpha channel to 1 regardless of provided color value
• Render a transparent badge to show incompatibility
• Update warning message to indicate opacity support
• Take opacity into account in color contrast calculations (if possible)

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[github-actions]

👋 Hey there. This issue hasn't had any activity for 180 days. We'll automatically close it if that trend continues for another week. If you feel this issue is still valid and needs attention please let us know with a comment.

[github-actions]

👋 Hey there. This issue hasn't had any activity for 180 days. We'll automatically close it if that trend continues for another week. If you feel this issue is still valid and needs attention please let us know with a comment.

[github-actions]

❌ We're automatically closing this issue due to lack of activity. Please comment if you feel this was done in error.

[github-actions]

👋 Hey there. This issue hasn't had any activity for 180 days. We'll automatically close it if that trend continues for another week. If you feel this issue is still valid and needs attention please let us know with a comment.

[github-actions]

👋 Hey there. This issue hasn't had any activity for 180 days. We'll automatically close it if that trend continues for another week. If you feel this issue is still valid and needs attention please let us know with a comment.