[C++ SDK] Create Rust side FFI bindings for the C++ SDK

[slbotbm]

Description

For C++ to utilize the Rust side code, bindings need to be created.

Component

None

Proposed solution

cxx will be used to create these bindings. There will only be one opaque type (IggyClient), which will be used to interact with the Rust code. Transparent types will include PolledMessages, Message, ServerDetails, TopicDetails, Identifier.

Integration tests will be written for the low level client created by these bindings.

Alternatives considered

uniffi

sub-issue of #2100