feat(project): Offer configPath property to workspace configs (workspace/1.1)

[maxreichmann]

JIRA: CPOUI5FOUNDATION-1233

---

This offers a configPath property to workspace dependency resolution entries as follows:

specVersion: workspace/1.1                      // new specVersion
metadata:
    name: default
dependencyManagement:
    resolutions:
        - path: ../test.library
          configPath: custom-config.yaml        // new customizable paths

(Introducing new specVersion workspace/1.1)

---

Other sub features:

• Improve error handling when path is absolute
• Forbid absolute paths for configPath
• Allow relative paths for configPath (for path it's already allowed)

[maxreichmann]

Kindly asking @KlattG to review the documentation part of this PR already (Workspace.md).

(I didn't add this feature to the usual migrate-v5.md because we planned to downport to v4 too)

[KlattG]

LGTM