docs: clarify variation_served uses variation key (dependent flags) - #731

Changed pages include:

• index.html - view
• 404.html - view
• bandit-quickstart/index.html - view
• contextual-bandits/index.html - view
• data-management/index.html - view
• experiment-analysis/index.html - view
• feature-flagging/index.html - view
• guides/index.html - view
• quick-starts/index.html - view
• sdks/index.html - view

There are more changes not included in the list