Exit SDK Methods

[HananINouman]

Problem:
Clients want a way to a way to exit a given validator on demand via their code.

Solution (This can be divided in smaller tasks):
Extract exit logic to sdk methods which can be integrated with any product. We mainly need three methods as Luke suggested:

• validateExitBlob: On POST, verify that a submitted partial-exit blob is correctly signed by the claimed operator
• recombineExitBlobs: Client-side function to stitch together a list of valid partial-exit blobs into a full exit message (This is same in both solutions), [TO DO] Check with Luke/Kalo the link they shared with me for this logic.