feat: fill msg timestamp while appending RLN proof it is not set

[chaitanyaprem]

Description

If message timestamp is not set, then as part of appending RLN proof to the message, the timestamp is also set based on which the RLN proof is calculated.

Fixes #926 and not just REST API but for all API's.

cc @waku-org/nwaku-developers This would have to be addressed in nwaku REST API as well.

[status-im-auto]

Jenkins Builds

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❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	2df3282	#1	2023-11-30 10:07:08	~1 min	nix-flake	📄log
✔️	40c0bb2	#2	2023-12-01 01:26:14	~1 min	nix-flake	📄log

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	da636bd	#3	2023-12-05 14:20:56	~1 min	nix-flake	📄log
✔️	c4db7df	#4	2023-12-06 01:50:34	~2 min	nix-flake	📄log

[richard-ramos]

The code looks okay, but I'm wondering why is it necessary to set the timestamp in the message?
AFAIK it's not used in the RLN validator, but instead the validation is done against the epoch attribute part of the RLN Proof

[chaitanyaprem]

The code looks okay, but I'm wondering why is it necessary to set the timestamp in the message? AFAIK it's not used in the RLN validator, but instead the validation is done against the epoch attribute part of the RLN Proof

True, but for Store queries to be consistent across nodes having a senderTimestamp helps with it.
Also this is already being tracked as an issue in nwaku at waku-org/nwaku#2193

More context regarding this can be found at https://discord.com/channels/1110799176264056863/1111540684575477821/1177574753100378123 as further improvements in store protocol also expects timestamp to be part of message. Hence it would help making it mandatory.