[wolf4ood]

What this PR changes/adds

• Service.
  • ParticipantContextService gets activateParticipantContext and deactivateParticipantContext.
  • updateParticipantContext keeps the stored state, so a PUT no longer resets it to CREATED.
  • ParticipantContext.toBuilder() now copies the identity. It was missing, which made toBuilder().build() fail.
• Management API v5. New admin-only endpoints (management-api:admin):
  • POST /v5/participants/{id}/activate;
  • POST /v5/participants/{id}/deactivate.
• Protocol API (virtual). A DEACTIVATED participant context is answered with 404, like one that does not exist:
  • by DspVirtualProfileDispatcher, which covers catalog, negotiations and transfers;
  • by /.well-known/dspace-version.

Why it does that

The participant context state was not enforced and could not be managed: only the management API authentication
filter checked DEACTIVATED (#6124), and any update reset the state (M5 in #6005).

Further notes

• Only DEACTIVATED blocks: CREATED keeps behaving as operational.
• Deactivation doesn't terminate anything. The state machines keep processing the ongoing negotiations and transfer
  processes, and they continue if the participant context is activated again.
• Admin calls on the resources of a deactivated participant context, and data plane signaling, are not checked.
• ParticipantContextService has two new methods. Custom implementations need to add them.

Who will sponsor this feature?

Please @-mention the committer that will sponsor your feature.

Linked Issue(s)

Part of #6005

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