Update tx docs to use api_version 2

[intelliot]

API version 2 is generally supported by all Mainnet rippled servers, as it was introduced in rippled 2.0.0 and multiple 2.0.0 amendments have already activated since then.

The docs should be updated to use api_version 2 because the format is more consistent with other methods.

• API version 2: https://github.com/xrplf/rippled/blob/develop/API-CHANGELOG.md#api-version-2
• tx docs: https://xrpl.org/docs/references/http-websocket-apis/public-api-methods/transaction-methods/tx#response-format

There are other api_version 2 changes which the docs should also be updated to reflect. I think it is ok to make the updates incrementally, but of course it is also fine to do it all at once, time permitting.