rpc: pass requests by value

[rockwotj]

Pass RPC requests by value, as we start to write some handlers using
coroutines, it can be a footgun to access have a suspension point, then
the request is destroyed. An example that motivated this:

ss::future<reply> service::handle(request&& r, rpc::streaming_context&) {
  co_await ss::coroutine::switch_to(get_scheduling_group());
  co_return co_await handle_request(std::move(r));
}

In this case r is destroyed because the coroutine does not own the
value, and handle request would have a stack-use-after-return issue.

Now that we pass by value, we don't have to remember to move the value
into the current method.

Fixes: https://github.com/redpanda-data/core-internal/issues/898

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v23.3.x
• v23.2.x
• v23.1.x

Release Notes

• none

[vbotbuildovich]

new failures in https://buildkite.com/redpanda/redpanda/builds/43498#018cdb8f-4871-4c46-9031-75627717886a:

"rptest.tests.recovery_mode_test.DisablingPartitionsTest.test_disable"
"rptest.tests.cluster_quota_test.ClusterRateQuotaTest.test_client_group_produce_rate_throttle_mechanism"

[bharathv]

nice

[rockwotj]

CI Failure: #15972

[vbotbuildovich]

ducktape was retried in https://buildkite.com/redpanda/redpanda/builds/43498#018cdcf4-c91a-4504-8509-4155b50501b6

[emaxerrno]

I wonder if we should enforce all types in RPC via a concept to be either small pods of say 16bytes or non copyable and non copy assignment.

[rockwotj]

Yeah not against making stuff explicitly copyable only, or doing this via serde where you have to add a flag to opt into copy constructor if not trivially copyable.