Add send flow warning on BSC

### Problem:
BSC users have been reporting loss of funds due to sending tokens to exchange addresses that don't support such token or the used network.

### Task:
Show a warning when the user is sending the selected token to the receiving address for the first time on Binance Smart Chain. The user will need to check the checkbox on the warning in order to continue.

### Resources:
[Design file on Figma](https://www.figma.com/file/EUQ1LPxKPU9tga4YnjISn1/Network-specific-assets?node-id=1594%3A21545)
[User story on Notion](https://www.notion.so/I-want-to-be-informed-that-the-tokens-I-am-sending-to-might-be-lost-if-the-recipient-address-doesn-t-8c34c5b7552946c49801c9c869f390ce)

Start by locating the token send flow for Binance Smart Chain and the state used to identify a first-time recipient. Use the linked Figma design and Notion user story to confirm the warning and checkbox behavior. Done means the warning appears for the specified first send and the transfer cannot continue until the checkbox is selected.

Written by the indexing model from the issue text.