Inconsistent workspace filter attribute naming across data sources

[grubmeshi]

Observation

The workspace filter attribute naming is inconsistent across data sources:

Data Source	Attribute Name	API Query Param
meshstack_building_block_definitions	workspace_identifier	ownedByWorkspace
meshstack_projects	workspace_identifier	workspaceIdentifier
meshstack_tenants	workspace	workspaceIdentifier

Proposal

For v1, settle on a single consistent naming convention for the TF schema attribute that filters results by owning workspace. Options:

1. workspace_identifier — explicit, matches the projects data source
2. workspace — shorter, matches tenants data source

The backend API is migrating toward ownedByWorkspace as the query parameter name (see meshcloud/meshfed-release#9921), but the user-facing TF attribute name should be consistent regardless of the underlying API param.

Context

Discovered during cross-workspace BBD data source work (meshcloud/meshfed-release#9921, #161).