fix: add missing ParticipantAgentExtension in IdentityAndTrustExtension

[bscholtes1A]

What this PR changes/adds

This PR registers a ParticipantAgentExtension in the IdentityAndTrustExtension that sets the ParticipantAgent.PARTICIPANT_IDENTITY attributes.

Without this attribute, all contract validations are failing (for example here as the ParticipantAgent.getIdentity() method would return null.

Why it does that

Enable proper contract validation when using IdentityAndTrustExtension.

Further notes

Also takes opportunity of this PR to add the missing counterPartyId in the catalog requests of the Participant fixture.

Linked Issue(s)

Closes # <-- insert Issue number if one exists

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[wolf4ood]

Can we make this extension optional? In dataspaces that are not using the did as participant id the identity extractor might
not be this one but a custom one

[bscholtes1A]

Can we make this extension optional? In dataspaces that are not using the did as participant id the identity extractor might not be this one but a custom one

Done, could you please review latest changes?