feat: use current timestamp when not provided in relay rest api

[chaitanyaprem]

Problem

When publishing a message via the REST API without setting a timestamp, default to the current one instead of 0 when RLN is enabled.

curl -X POST "http://127.0.0.1:8645/relay/v1/auto/messages"
-H "content-type: application/json"
-d '{"payload":"XQ==","contentTopic":"/my-app/2/chatroom-1/proto"}

Note: Also need to make this mandatory in Relay publish API if RLN is enabled, else need to set it to currentTimestamp.

[chaitanyaprem]

Weekly Update

• achieved: return error in relay API when message gossipsub threshold is crossed, fill messageTimestamp if RLN is enalbed and not set in WakuMessage, improve errors returned for filter unsubscribe APIs