Introduce `Rc` with custom allocator

## Brief feature description

With the `Rc` approach in #100 we introduced heap usage. We need a central construct that owns a custom allocator and provides the allocator to the underlying constructs, namely `Rc`.

Therefore, we need an `Rc` that can be created with `Rc::new_in` and acquires the memory from the custom allocator. See the new `allocator_api` of rust, https://github.com/glandium/allocator_api/ and https://doc.rust-lang.org/std/rc/struct.Rc.html#method.new_in

By default, the `iceoryx2-bb-posix::heap_allocator::HeapAllocator` shall be used. The used allocator trait shall be `iceoryx2-bb-elementary::allocator::BaseAllocator`.

Start by reading the Rc approach in issue #100, then compare Rust's allocator_api and Rc::new_in behavior. Trace how iceoryx2-bb-posix::heap_allocator::HeapAllocator and iceoryx2-bb-elementary::allocator::BaseAllocator are intended to interact with Rc. Done means Rc::new_in acquires memory from the supplied custom allocator and uses HeapAllocator by default.

Written by the indexing model from the issue text.