[PLAT-6805] Adding support for Fixed/OIS swaps

Support for par rate calculation exists for all fixed-float swaps but
the converter from financial security to swap definition does not
process fixed-float swaps to a fixed-float swap definition if the index
is other than ibor.

This PLAT adds the support for swap with floating leg with OIS index.
Would be good to add some unit test examples in InterestRateSwapFnTest, note there is a test called fixedVsOnCompoundedSwapParRate() which can be enabled. The expected par rate here matches the SwapCalculatorE2ETest.