Introduce `Capacity` type

[elfenpiff]

(Code) Example Of Cumbersome API

Fixed size containers often have a capacity member variable that is never changed during their lifetime. A custom strong type that can be only set once with new and can be read via Deref would reflect this in the API.

Improvement Suggestion

• [ ] Introduce Capacity type in iceoryx2-bb-elementary
• [ ] Use Capacity type in every RelocatableContainer, Container

[elfenpiff]

@elBoberido I think I would close the issue without fixing it, since such a type would have severe drawbacks.

• If we implement copy & clone the sole purpose, modify once and never update can be easily circumvented
• If we do not implement them, every container using this type is suddenly also non-copy & non-clonable.

We can implement clone by hand, but loosing copy would be a pity.

[elBoberido]

@elfenpiff fine with me