Add command for getting arbitrary ledger entries

[leighmcculloch]

The contract read subcommand supports reading contract data ledger entries, but not other ledger entries outside of contract data. It accepts a contract data key, and returns a contract data entry.

It'd be helpful if it could retrieve any ledger entry, and I think there is mild ecosystem demand for this.

I've seen several people spread over a long period of time (untracked sorry, without links) try to use the contract read subcommand for reading random entries, or for reading contract data ledger entries and expect to get back the full entry as XDR, not only the value.

It seems like the existing UI maybe underestimated the average user's willingness to engage with the ledger entry as a whole, or at the least there's a second audience of users who are interested in working with ledger entries themselves.

The RPC has a getLedgerEntries endpoint that given multiple keys returns multiple entries. It would be trivial to support that in the CLI as a subcommand. The less trivial thing would be to consider where to put it.

[leighmcculloch]

Suggestion for API:

stellar ledger-entries get --key-xdr <XDR> | stellar xdr decode --type LedgerEntry

[janewang]

Related to this ticket #1838