Feature/css customization v3

[sushmi21]

Success criteria

Please describe what should be possible after this change. List all individual items on a separate line.

• Add missing classes to css-customization document
• Rename some classes to have meaningful and appropriate names

How to test

Please describe the individual steps on how a peer can test your change.

1. Newly introduced classes are added to the css-customization document
2. webchat-chat-options-root is renamed to webchat-chat-options-action-btns-root
3. webchat-chat-options-button is renamed to webchat-chat-options-action-button
4. webchat-chat-options-button-container is renamed to webchat-chat-options-action-button-container

NOTE: The renaming can have breaking style changes for some customers. This should be mentioned in the release notes

Security

• Possible injection vector
• Authentication/Access controls touched
• Sensitive Data could be exposed
• XSS
• Logging/Monitoring touched
• Exchanges data with external systems
• No security implications

Additional considerations

• This PR might have performance implications