feat: Implement libp2p-mix and integrate with lightpush in js-waku

[chaitanyaprem]

Description

As explained here, in order for libp2p-mix protocol to be used in js-waku there are 2 main implementations that need to be done.

Note that mix implementation should allow easy integration of any existing req-resp protocol to use mix with minimal changes to the API and protocol implementation.

User Story

js-mix specific items (Still require detailed analysis to identify if anything else is required)

• Mix implementation in js. (Either it is part of js-libp2p or separate repo TBD)
• Implement EntryConnection abstraction
• Implement Send functionality equivalent to AnonymousLocalSend
• Implement a mix node pool and its maintenance logic which can be integrated with discovery protocols in upper layer(js-waku)
• Implement reply logic ie building SURB and processing of SURB

js-waku specific items

• Node initialization to support option to enable mix and perform initializing functions
• Lightpush API to be updated to support an option to send using mix
• Publish lightpush messages via mix.
• Use preconfigured mix nodes
• Use discovered mix nodes and maintain a local mix node pool
• Replies for lightpush also use mix SURB.
• Integrate Store to use mix
• Have an app that helps in dogfooding mix (maybe a chat app)

Proposed Solution / Feature Design

TBD

Optional: Diagram or Draft of Design

TBD

Notes

• libp2p-mix spec
• Waku-Mix spec
• mix implementation in nim.
• forum post discussing some details
• nwaku mix integration issue
• Waku-mix implementation in nwaku