nix: create initial version of flake

[markoburcul]

It includes also androidndk and files needed for nimbus-build-system

Referenced issue: #3232

Description

Adding Nix flake to build Android app library

How to test

1. nix build '?submodules=1#'

Issue

#3232
closes #

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Details:

Unknown release type "nix" found in pull request title "nix: create initial version of flake".

Available types:

• chore
• docs
• feat
• fix
• refactor
• style
• test

[markoburcul]

I've managed to overcome building the Nim compiler using nimbus-build-system. The issue I've encountered is that nwaku is using Nim 2.0.12 while for nim-codex it is 2.0.14. The part in the preBuild phase that had to be added is a bit different:

    pushd vendor/nimbus-build-system/vendor/Nim
    mkdir dist
    cp -r ${callPackage ./nimble.nix {}}    dist/nimble
    chmod 777 -R dist/nimble
    mkdir -p dist/nimble/dist
    cp -r ${callPackage ./checksums.nix {}} dist/checksums  # need both
    cp -r ${callPackage ./checksums.nix {}} dist/nimble/dist/checksums
    cp -r ${callPackage ./atlas.nix {}}     dist/atlas
    chmod 777 -R dist/atlas
    mkdir dist/atlas/dist
    cp -r ${callPackage ./sat.nix {}}       dist/nimble/dist/sat
    cp -r ${callPackage ./sat.nix {}}       dist/atlas/dist/sat
    cp -r ${callPackage ./csources.nix {}}  csources_v2
    chmod 777 -R dist/nimble csources_v2
    popd

In nimbus-build-system the directory vendor/Nim was missing rightly placed atlas and sat git repositories.

[jakubgs]

Seems a bit different than what we had when nimbus-eth2 was using Nim 2.0.12, but if it works it works.