Add add_all_liquidity omnipool extrinsic

[green-jay]

Similarly to #1238, where new extrinsic to remove_all_liquidity was introduced, it would be useful to have the opposite, where all available balance of an asset would be added as LP.

This would be useful e.g. for scenarios where a position is removed (unknown balance is released) and then re-added as it would not be necessary to know any amounts beforehand.

[enthusiastmartin]

this should pretty straightforward and quick thing to add.