[WIP] feat: Token search

[ziad-saab]

Description

Related issues

Fixes:

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Screenshots/Recordings

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[gambinish]

If a user searches for a token on a network not yet added to their account, we won't have some data needed to handle certain fiat conversion throughout the app (for instance, on AsssetOverview)

From a technical perspective, this may require us to add the required chain to the NetworkController state whenever you TokensController.addSearchedToken(), so that the networkConfigurations.[chainId].nativeCurrency for the fiat conversion is also available for the UI to consume.

We will likely also want to handle the network switch on behalf of the user, so that the correct network appears below the ticker on the TabView:

Slack conversation for reference