FixedCouponBond model should represent redemption value

There are still active govt bonds which have a redemption value other than par e.g. IT0000366655 which has a redemption value of 99.909.

Once the object model can support this there are various yield calculations which will need to be updated to use this redemption value rather than 1 e.g. https://github.com/OpenGamma/Strata/blob/653ec06bf7efcb63240c97f85546f5a30df7f955/modules/pricer/src/main/java/com/opengamma/strata/pricer/bond/DiscountingFixedCouponBondProductPricer.java#L580

(ignoring the fact that Italian bonds need further modifications…)