chore(rln-relay): use the only key from keystore if only 1 exists

[rymnc]

Description

from the perspective of an end user, i will most likely have only one membership per chainId-contractAddress pair.
To account for this, we are removing rln-relay-membership-index as a compulsory argument to wakunode2, and instead, using the only available key in the keystore

Changes

• Changes to the keystore to account for this
• Updated tests
• Updated config of wakunode2 and chat2 to make it an Option type
• Updated OnchainGroupManager init process to set the membershipIndex appropriately

How to test

1. Create a fresh keystore using rln-keystore-generator - contractAddress: 0x0A988fd9CA5BAebDf098b8A73621b2AaDa6492E8
2. Run wakunode2 with the following args

./build/wakunode2 \
--rln-relay=true \
--rln-relay-dynamic=true \
--rln-relay-cred-password=$KEYSTORE_PASSWORD \
--rln-relay-cred-path=rlnKeystore.json \
--rln-relay-tree-path=rln_tree_new_1.db \
--rln-relay-eth-contract-address=0x0A988fd9CA5BAebDf098b8A73621b2AaDa6492E8  \
--rln-relay-eth-client-address=$SEPOLIA_URL \
--nodekey=161c2836197e8918d7eb1039758423795f0dc697a018ed55d5931aa9b0e5efb3 \
--log-level=debug

You should see that it is able to fetch the membership index from the decrypted keystore. Additionally, the rpc api is able to append proofs to messages as well.

Issue

Addresses a part of #1906

[github-actions]

This PR may contain changes to configuration options of one of the apps.

If you are introducing a breaking change (i.e. the set of options in latest release would no longer be applicable) make sure the original option is preserved with a deprecation note for 2 following releases before it is actually removed.

Please also make sure the label release-notes is added to make sure any changes to the user interface are properly announced in changelog and release notes.

[github-actions]

You can find the image built from this PR at

quay.io/wakuorg/nwaku-pr:1984

[rymnc]

this is quite ugly - the compiler was throwing errors when i tried doing this -

keystoreCredential = keystoreCredentials.getFields().values()[0]

[vpavlin]

Isn't that because values() returns iterator, which means you'd have to turn it into seq first before you can access the Nth element?

[rymnc]

thanks, addressed in 99b3fe6!

[alrevuelta]

lgtm! thanks!