[BC Idea]: Support multi-company setup for External SharePoint accounts

BC Idea Link

https://experience.dynamics.com/ideas/idea/?ideaid=077211df-5b35-f011-a2da-7c1e52b4c1ef

Description

Description of the problem

When Microsoft External File Storage is configured to use SharePoint, the SharePoint setup must currently be configured separately for each company.
In many Business Central environments, multiple companies belong to the same organization and use the same SharePoint tenant, the same application registration, and the same certificate-based authentication setup. Despite sharing the same configuration, administrators must manually maintain identical SharePoint settings in every company.
This creates unnecessary setup and maintenance effort, especially in larger environments. Some organizations operate more than 50 companies within a single Business Central tenant. In these scenarios, the same SharePoint configuration may need to be entered and maintained dozens of times.
Besides the administrative overhead, this increases the risk of inconsistencies and configuration errors between companies and makes ongoing maintenance more time-consuming than necessary.

Description of the solution

Allow the SharePoint connection configuration to be defined once and shared across companies.
This would enable organizations that use a single SharePoint tenant and authentication setup to maintain one centralized configuration instead of duplicating the same setup in every company.
Company-specific document storage structures can still be managed through the existing document location configuration, while the connection details themselves only need to be maintained once.

Additional context
This is a common requirement in larger multi-company Business Central environments where many companies share the same SharePoint infrastructure and authentication setup.

I will provide the implementation for this BC Idea

• I will provide the implementation for this BC Idea
  Internal work item: AB#580696

No files, tests, or entry points are named. Start by tracing the existing Microsoft External File Storage and SharePoint configuration, then compare how connection details and document locations are stored per company. Done means shared connection settings can be maintained once while company-specific document locations continue to work.