Rails: Use shared namespace if present in agent configuration while creating a new workspace

MR: Pending

Description

Currently, when a new workspace is created, we generate a new namespace for it. However, if the user has provided the shared_namespace field in the associated agent configuration, we should instead use that while creating a new workspace.

Acceptance criteria

• If the associated agent's shared_namespace field is not nil, use that value for the new created workspaces namespace attribute instead of using a random string.

Implementation plan

• Update RemoteDevelopment::WorkspaceOperations::Create::Creator to use the associated agent's shared_namespace field if it is not nil.