bug(core) CDB-833: Retry Getting Transaction

[dbcfd]

Brings in exponential backoff package to provide exponential backoff behavior when we fail to get a transaction from the anchor. Adds 1 test and updates 1 test to verify this behavior.

[linear[bot]]

CDB-833 Add retries when loading transactions from ethereum

EthereumAnchorValidator._getTransactionAndBlockInfo() should have retries in case we get a temporary error from the ethereum provider

[stbrody]

@dbcfd what's the status of this PR? Should we close it?