Temporarily fix compatibility for SchemaResult

[skejserjensen]

This PR adds a temporary workaround for issue #2445 in arrow-rs by extending FlightService.get_schema() to always prepend both the 32-bit continuation indicator and the 32-bit little-endian length to SchemaResult.schema so it can be deserialized by the other Apache Arrow Flight implementations. To preserve compatibility with the Rust client (mdb), execute_command() have been extended to strip the first eight bytes of SchemaResult.schema. I have manually tested the changes with Go (using the code in Telegraf-Output-Apache-Arrow-Flight), Java, Python, and the Rust client (mdb) using multiple different schemas. Finally, while slightly outside the scope of the PR, I have moved DoExchangeStream before DoActionStream so the order of the types should match the order of the methods that use them in FlightService.

[skejserjensen]

Based on the discussion in the two issues I have updated the PR to serialize and deserialize the Schema to IpcMessage but use SchemaResult as the transport format as required by the return type of get_schema(). The associated functions syntax is used for try_from() in the client to disambiguate between different methods.

[agneborn98]

This looks a lot better and is definitely less "hacky". I have tested it on my computer as well and ran into no issues, so this solution works fine.