Token detection for Ethereum Mainnet

[Cal-L]

Description

This is a continuation on MVP for auto token detection. For now, we're scoping down token detection to only work for Ethereum Mainnet. The token detection toggle in Experimental settings should hide for testnets + custom networks.

Technical Details

• Hide the token detection toggle for anything other than Ethereum Mainnet.
• Turn off toggle by default
• Move toggle over to Experimental
• For Ethereum Mainnet in token search, add token detection info banner as header
• Add analytics events for toggling token detection toggle. Token detection turned ON & Token detection turned OFF. Provide chainId property.

Acceptance Criteria

• Token detection toggle should be hidden for all networks other than Ethereum Mainnet.
• Tokens should be auto detected on Ethereum Mainnet, when token detection is on (user opts in).
• Token search in Add Tokens should return dynamic list from API if token detection is on. Otherwise, returns static list of tokens.
• Test analytics events for token detection toggle on & off

References

• Figma link here - https://www.figma.com/file/HgRPmjjq8Y6cmtewnsuFDF/Extension-Token-Detection?node-id=617%3A3477