Policy interface update

[aalavandhan]

Added cpi and exchange rate getters

[openzeppelin-code]

Policy interface update

Generated at commit: e3931381cff3948a708dbf6166ac37331ed2e610

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	1 1 0 5 23 30
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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[brandoniles]

I think we should add getTargetRate() to the IAmpleforth interface.

But don't think we need getExchangeRate()

[brandoniles]

LGTM