Allow users to go short even if they have some long position and vice versa by changing hard block into overrideable warning

[alexisgauba]

Please describe the problem you're having.
Currently we only allow users to go short if they have closed out their full long and vice versa. However, many advanced users (especially ones that LP) can be long and short at the same time or have just amounts of either. Instead of hard blocking this scenario, we can have a warning that warns users they are going long while they still have a short or vice versa, which serves the purpose of preventing most people from taking that action, but doesn't frustrate or block advanced users who want access to that flow.

Screenshots
Turn this into a warning instead of a hard block. Same for if a user has a short position and is trying to go long. We can use the same format we use for high slippage where we outline the bottom button in red and say "trade anyway"

Additional context
https://opyn.slack.com/archives/CKKRBUXNZ/p1654458636837849