A node that handles REST-Store requests normally acts as a
Store-client and therefore it retrieved the messages from another
Store-node.
With these changes, we allow a node with Store mounted, to retrieve
its messages. In other words, the node can act as a Store-server of
its messages.
* test_rest_store.nim: add a new test to validate that the self-node can
retrieve its messages to the REST client.
* rest/store/client.nim: add new proc to allow making a GET store
request without peerAddr.
* rest/store/handle.nim: add logic to handle requests that don't
provide peerAddr but the self/local node has Store mounted. In this case,
the self/local node will retrieve its locally stored messages.
* waku_store/self_req_handler.nim: logic to handle "store" requests
allowing the REST-store node to act as a Store-server node. The
'self_req_handler.nim' helps to bypass the store protocol and directly
retrieve the messages from the local/self node. I added this logic in
a separate file from 'protocol.nim' because it doesn't participate in
any libp2p communication.
* waku_store/protocol.nim: make 'queryHandler' attribute public so that
it can be used from the 'self_req_handler.nim' module.