Investigate support for concurrent orders

[sadhbh-c0d3]

• Find out what will happen if we allow concurrent orders from same user
• Check how index order manager will cope with this
• Check how collateral is accounted
• Check how batch creating works
• Check how batch processing works
• Check how minting works

At present we have two queueing systems in place:

• Index Order Manager: uses one queue for each pair (Chain Address x Index Symbol)
• Solver: uses one queue for each Chain Address

Additionally Collateral Manager tracks deposits per Chain Address and does not have any split by Index Symbol (might be needed to reflect for OTCCustody is split between OTCIndex tenants)