Generate Witness Data in IAVL tree by tracing operations

[Manav-Aggarwal]

We'd like to add tracing for keys accessed in the IAVL tree along with the operation itself during the following operations:

• Set
• Get
• Remove

For each operation above, the keys accessed should be used to generate the existence proofs needed for performing the said operation.

Overall, after performing a bunch of operations, an IAVL tree should have the following struct inside it to record all the operations and existence proofs required for each operation:

type WitnessData struct {
	Operation Operation
	Key       []byte
	Value     []byte
	Proofs    []*ics23.ExistenceProof
}

Also, add an option to enable/disable tracing in an IAVL tree.