Identity Hub: initial integration

[marcgs]

What this PR changes/adds

Integrate IdentityHub into MVD. At the moment the identity hub is not seeded with any Verifiable Credentials. An integration tests verifies that the IdentityHub endpoints are accessible, and that these return an empty set of VCs.

Why it does that

First step of IdentityHub integration.

Linked Issue(s)

https://github.com/agera-edc/IdentityHub/issues/21

Checklist

• [x] added appropriate tests?
• [x] performed checkstyle check locally?
• [x] added/updated copyright headers?
• [x] documented public classes/methods?
• [x] added/updated relevant documentation?
• [ ] added relevant details to the changelog? (skip with label no-changelog)
• [ ] formatted title correctly?