slashing: enshrine the slashing program

[AshwinSekar]

Problem

The slashing program will initially be deployed to S1asHs4je6wPb2kWiHqNNdpNRiDaBEDQyfyCThhsrgv a key that I own.
We wish to enshrine the program at S1ashing11111111111111111111111111111111111 and require that further updates be made via a feature gated validator change.

Summary of Changes

On the first epoch that create_slashing_program: sProgVaNWkYdP2eTRAy1CPrgb3b9p8yXCASrPEqo6VJ is activated:

• Verify that the verified build hash of the deployed program matches the expected hash computed from the spl-slashing v.1.0 release
• Clone the program account, and set the program data address to point to the PDA of the enshrined address
• Clone the program data account, set the upgrade authority to the system program
• Write these cloned accounts at the enshrined address and PDA respectively