feat: initialize IssuerMetadataSynchronizationPolicy

[nanderstabel]

Description of change

This PR introduces the IssuerMetadataSynchronizationPolicy in the Issuance domain that will listen for specific TemplateEvents from the Library Domain. In a near future update this policy will dispatch ServerConfigCommands in order to update the Credential Issuer Metadata in order to keep the credential_configurations_supported field in sync with the Templates stored in agent_library.

In order to facilitate this, the Policy needs a reference to the IssuanceState:

pub struct IssuerMetadataSynchronizationPolicy {
    // TODO: Actually use this.
    _issuance_state: Arc<IssuanceState>,
}

This meant that ApplicationState cannot have sole ownership anymore over IssuanceState and therefore it has been wrapped into an Arc. The result of that is that many files in agent_api_rest had to be updated in order to wrap the state into Arcs.

This PR also includes a fix for the HTTP Response of the GET /v0/templates/ and GET /v0/templates/<template_id> endpoints that ensures that the responses are returned in camelCase.

Links to any relevant issues

• Template management #202

How the change has been tested

• Since this merely an initialization of the Policy the only real 'proof' of the code working is that it compiles. The actual workings of the Policy will be implemented in feat: derive credential configurations from templates #245
• camelCase responses are tested through test_template_response_serialization.

Definition of Done checklist

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• I have commented my code, particularly in hard-to-understand areas
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• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have successfully tested this change in a docker environment