Return friendly error when AMQP 1.0 receiver has no source (backport #15147)

[mergify]

When a client attaches an AMQP 1.0 receiver link without specifying a source address, RabbitMQ crashes with a function_clause error and returns an Erlang stack trace to the client. This makes it difficult for developers to understand what went wrong.

Previously, the client received:

SessionError: function_clause
[{rabbit_amqp_session,ensure_source,
     [undefined,false,<<...>>,<<...>>,
      {user,<<...>>,[administrator],[...]},
      <<...>>,<0.585.0>,[],[]],
     [{file,"rabbit_amqp_session.erl"},{line,2665}]},
 {rabbit_amqp_session,handle_attach,2,...},
 ...]

This change adds a new clause to ensure_source/9 that catches the case where the source is undefined. Instead of crashing, the function now returns {error, source_address_required}, which handle_attach/2 maps to an amqp:invalid-field error with a clear message.

Now, the client receives:

LinkError: Attach refused: source_address_required
  condition: 'amqp:invalid-field',
  description: 'Attach refused: source_address_required'

The error condition amqp:invalid-field is appropriate here because the client failed to provide a required field in the attach frame, not because a resource was not found.

Fixes #14300

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This is an automatic backport of pull request #15147 done by Mergify.