Set state to ACTIVE when creating new key pairs

[paullatzelsperger]

Bug Report

Describe the Bug

When new key pairs are created via the Management API, their state is set to CREATED, but never advances to ACTIVE.

Possible Implementation

• When creating a participant, the key pair that was created alongside them should be set to ACTIVE.
• The KeyPairDescriptor gets a new field isActive, which determines whether a key pair is set to ACTIVE or CREATED. defaults to true
• When a new key pair is created, and the isActive flag is false, and the participant does not have an active keypair, a warning is logged
• The key pair management API gets a new method POST "/v1/participants/{participantId}/keypairs/{keyPairId}/activate" that allows a state change CREATED -> ACTIVE, and returns a 400 in all other cases.