AsyncAPI 2.x: additional non-concrete elements for binding objects

[char0n]

Following binding objects do have nested objects for their fixed fields. These nested objects are currently not easily identifiable by element or class. In order to provide remediation for this Non Concrete Elements (NCEs) needs to be introduced to allow create linting rules in apidom-ls. I have identified that the level of nesting is maximally: 1.

• AMQP 0-9-1 Channel Binding Object
• IBMMQ Channel Binding Object
• MQTT Server Binding Object
• Solace Operation Binding Object

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We currently only validate top level fixed fields in all binding objects. Nested objects as currently not validated as they don't have NCEs.

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Identified in #1647