Add native usdc to op, arb, and polygon (#595)

Signed-off-by: Alex Gaines <[email protected]>

UPPs/upp-15.md

@@ -0,0 +1,23 @@
+## Status
+
+Draft
+
+## Summary
+
+This UPP proposes adding native USDC for use as collateral in UMA contracts on Optimism, Polygon, and Arbitrum.
+
+## Rationale
+
+Bridged USDC is currently approved as a collateral currency on Optimism, Arbitrum, and Polygon. Native USDC is already approved on Ethereum mainnet and Avalanche. 
+
+This UPP is proposing to update Optimism, Polygon, and Arbitrum to include native USDC.
+
+## Specifics
+
+To implement this upgrade, a final fee of **250** needs to be added for the following addresses in the Store contract on Optimism, Arbitrum, and Polygon:
+
+-   USDC Optimism: [0x0b2C639c533813f4Aa9D7837CAf62653d097Ff85](https://optimistic.etherscan.io/token/0x0b2C639c533813f4Aa9D7837CAf62653d097Ff85)
+-   USDC Arbitrum [0xaf88d065e77c8cC2239327C5EDb3A432268e5831](https://arbiscan.io/address/0xaf88d065e77c8cC2239327C5EDb3A432268e5831)
+-   USDC Polygon [0x3c499c542cef5e3811e1192ce70d8cc03d5c3359](https://polygonscan.com/address/0x3c499c542cef5e3811e1192ce70d8cc03d5c3359)
+
+