Update LP Interface

[trmid]

No description provided.

[linear]

GEN-633 Allow Liquidation Pairs to be discoverable

To check if a liquidationPair is active, a bot must check if the liquidationPair's source points back to it, but there is no standard for this.

• Add to ILiquidationSource the fxn isLiquidationPair(address tokenOut, address liquidationPair) to determine whether liquidation pair is valid (so we can verify)
• Add an event to ILiquidationSource that must be emitted when a liquidation pair is set (so we can index)

[github-actions]

LCOV of commit 30a1087 during 100% Test Coverage #162

Summary coverage rate:
  lines......: 100.0% (140 of 140 lines)
  functions..: 100.0% (29 of 29 functions)
  branches...: no data found

Files changed coverage rate: n/a