rpc: Add diagnostic events to sendTransaction response

[2opremio]

What

Add new diagnosticEventsXdr field to sendTransaction's RPC method response.

Closes #1157

Similar to stellar/go#5148

Also, use the new Core ENABLE_DIAGNOSTICS_FOR_TX_SUBMISSION flag in integration tests.

Why

Improve debug-ability of Soroban transaction submission.

Known limitations

N/A

[sreuland]

this core cfg needs to be added to rpc's captive core instance for any deployment correct? I assume is the case, we'll need to update the rpc deployment manifests on kube to include this and i spun up quickstart/#543

[2opremio]

It doesn’t need to be captive core specifically. It should be added to any core instance you are sending transactions to, and only if the more general ENABLE_SOROBAN_DIAGNOSTIC_EVENTS isn’t already enabled (@dmkozh please confirm whether this is correct)

Edit: read @dmkozh ’s comment below for a full description

[dmkozh]

only if the more general ENABLE_SOROBAN_DIAGNOSTIC_EVENTS isn’t already enabled

These flags are independent and control different things. Here is the brief description:

ENABLE_SOROBAN_DIAGNOSTIC_EVENTS:

• Adds the apply-time diagnostic events to the tx meta stream
• Meaningless if tx meta is not enabled and is not allowed at all on validator nodes
• Should be enabled for the captive core nodes that are being used for tx meta ingestion

ENABLE_DIAGNOSTICS_FOR_TX_SUBMISSION

• Adds the diagnostics directly to the Core's tx endpoint JSON response.
• The diagnostics are only populated for the transactions that get immediately rejected by Core (i.e. they don't have a chance to be applied)
• Can be enabled on any node, including validators
• Should be enabled on the nodes which accept transactions (from Horizon/soroban-rpc). Typically these are not captive core nodes, but in some setups I can imagine both flags being enabled (notably, for standalone network mode both flags are useful).

[sreuland]

@dmkozh , awesome, thanks for further clarification, yes, in some deployment configs, the captive core instance is the node used for tx sub. btw, is there a separate core cfg variables doc that has this same content for ref?

[dmkozh]

It doesn't seem like we have a doc like that, but we have inline comments for most of the configuration flags in the example config (https://github.com/stellar/stellar-core/blob/f9999b8d31aef2b3e96226685b55a8506ba3c721/docs/stellar-core_example.cfg#L610). I'll open an issue to update it with the new soroban-related flags.

[sreuland]

lgtm, left comment on thoughts for propagating the new api field to upstream(docs, sdks).