Add OvernightOvernightSwapCurveNode

[marc-henrard]

Several SwapCurveNode are available to calibrate curve, including IborIbor and OvernightIbor. A new type with OvernightOvernight would be important to calibrate to new benchmarks like SOFR and ESTER were the initial market will probably be in basis swap EFFR-SOFR and EONIA-ESTER. This will require the creation of the associated Template and Convention.

[mozzinho]

Is there any plan to implement this for Isda IR curves? I.e. in respect of CDS. I don't see an appropriate subtype of SwapIsdaCreditCurveNode.