chore: deprecate import in rln-js

[weboko]

Idea is to remove import field for RLN credentials.

More details - #225 (comment)

[fryorcraken]

Might make sense to do waku-org/js-rln#48 first so that we can have 2 examples:

1. Uses wallet signature to generate/retrieve credentials
2. Uses import/export tool to manage credentials, this would enable user to use credentials across implementations

[fryorcraken]

Actually, being able to export credentials when they are created from a signature would be useful.

Currently, you have to pass your private key to nwaku to register in the RLN contract. This is not great as your private is seen clear text by your computer (shell history or config file).

Instead, one could be encouraged to use Web app to register in RLN contract, and then export the RLN credentials to use them with nwaku. Cc @rymnc, wdyt?

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We are attempting 2 things with the examples:

• PoCs
• Examples for developers

Theses two goals are contradictory. First we should review how we want to use examples for Dev Rel. @fryorcraken to discuss with @hackyguru and @LordGhostX.

[rymnc]

Great idea. Please refer to the waku keystore to generate a valid keystore that can be accepted by nwaku - https://github.com/waku-org/nwaku/tree/master/waku/v2/waku_keystore

adapted from nimbus' keystore, should be some code you can reuse

[fryorcraken]

Tracking here the PoC vs examples discussion: #163 (comment)