Move dependencies to extras

What

Remove hard dependency on openassetio and openassetio-mediacreation and move to extras

Why

openassetio should always be provided by the host runtime (to ensure we don't have multiple copies loaded simultaneously). Having it as a hard dependency anywhere up the stack causes problems, as pip will try and provision it too, which usually results in a separate static build being installed in addition to whatever the host provides (unless the host is pure python).

ACs

• openassetio moved to a extras dep under the all and deps names
• openassetio-mediacreation moved to an extras dep under the deps name. [TBC]

Comienza localizando la configuración de las dependencias del paquete e inspecciona cómo están declarados los requisitos existentes de openassetio y openassetio-mediacreation. Verifica que openassetio esté disponible mediante los extras all y deps, y que openassetio-mediacreation esté disponible mediante deps; resuelve la incertidumbre señalada antes de considerar terminado el trabajo.