Refactor flake and overlay

[jonringer]

Thought it was awesome that you guys using nix, so I thought I would help with some minor improvements:

• Move added packages into their own files
• Expose legacyPackages, overlay, and overlays attr in flake output
• Use protobuf3_15 instead of override
• Add devShell to overlay

Some non-obvious changes:
Using packages (or nativeBuildInputs) instead of buildInputs for mkShell allows for XDG_DATA_DIR to be set with the shell-completion files of the added packages, so you should get tab completion if you use bash completion (IIRC, fish and zsh don't respect XDG_DATA_DIR) related nixpkgs PR

Otherwise, not much has changed from a nix perspective. Just two renames:

jon@jon-desktop /home/jon/projects/waypoint (main)
$ nix eval .#devShell.x86_64-linux.drvPath
"/nix/store/yr303a78g6gh4q7g9cbf96ls6f0bal0x-waypoint.drv"

jon@jon-desktop /home/jon/projects/waypoint (refactor-nix)
$ nix eval .#devShell.x86_64-linux.drvPath
"/nix/store/f3ix16p436x3wci8cn1drhs93hg8gq64-waypoint.drv"

jon@jon-desktop /home/jon/projects/waypoint (refactor-nix)
$ nix run nixpkgs#nix-diff /nix/store/yr303a78g6gh4q7g9cbf96ls6f0bal0x-waypoint.drv /nix/store/f3ix16p436x3wci8cn1drhs93hg8gq64-waypoint.drv
- /nix/store/yr303a78g6gh4q7g9cbf96ls6f0bal0x-waypoint.drv:{out}
+ /nix/store/f3ix16p436x3wci8cn1drhs93hg8gq64-waypoint.drv:{out}
• The set of input derivation names do not match:
    - go-protobuf-v1.5.2
    + go-protobuf-1.5.2
• The environments do not match:
    buildInputs=''
    /nix/store/2y8p2cx4xabvf1hf810s9zb6cb0bx9mc-docker-compose-1.29.2 /nix/store/sppqwgfpqhjl1lk90gxfdyx2jqxbbfwk-go-1.16.7 /nix/store/hlpk5jjw7f2skknlwh7z2gc0c9qnckl7-go-bindata-3.22.0 /nix/store/gz46hwrdjx9i8gxgkia20ayb2nhyf5vy-grpcurl-1.8.2 /nix/store/dih2gzb715q5k8hw7qjmq0n35ba30pb0-nodejs-16.6.1 /nix/store/g1yan04fzg018134jyz5g36439jd4b3d-postgresql-12.7 /nix/store/zgagnpjcpi2zvimmswrv6pf91svjfjf0-protoc-gen-doc-unstable-2019-04-22 /nix/store/s4lqvzb04xvcdijwq2cancpwvi1807bn-protobuf-3.15.8 /nix/store/bly9bmpxhmick415qrasgfvjdj4y5rn3-go-protobuf-v1.5.2 /nix/store/ccd1xjg0p9r23k1i9cpxx9zf7rr36r17-go-protobuf-json-069933b8c8344593ed8905d46d59c6647c886f47 /nix/store/m8n43fdmfnl24d8yh90r9l0xa1w3zvlz-go-tools-35839b7038afa36a6c000733552daa1f5ce1e838 /nix/store/ln0f156f6qcdf15j6gy2mjw263s2clwg-go-mockery-1.1.2 /nix/store/vjx713gmz1qqzllvppnl02f4zpza5gl8-go-changelog-56335215ce3a8676ba7153be7c444daadcb132c7 /nix/store/4mqvyh5q93ja860656bi0q9sg5sqhqs4-doctl-1.63.1 /nix/store/cx42syr9krm4f7hip1za88lr0gmw7y9q-kubectl-1.22.0 /nix/store/3d8z7x0p3fzhjkxdfr3cg6vfkfmqadnd-pkg-config-wrapper-0.29.2 /nix/store/2racw0r4a6f1ya6hv7a47w544cgarcjf-autoconf-2.71 /nix/store/9wgw1bxavq7d4hj3igw8mm4l68vrp5bh-automake-1.16.3 /nix/store/kxi9r99hgdq1bi7ma135pbn7p3jqlmdk-libtool-2.4.6 /nix/store/gr6hd0mba0217fp8msgmj8sp6a2wn6bh-nasm-2.15.05 /nix/store/jklgf34m49dl7fq5xy3b55szy5zjpq2f-autogen-5.18.16-dev /nix/store/mzpfnpbax7i5b8ipsgf27i7nlmnhpvn3-zlib-1.2.11-dev /nix/store/xmdhdglf79q6f5hg9yqbdbzfbrfl9k5v-libpng-apng-1.6.37-dev /nix/store/dbcd4ivx25dqdiq2p95z8q0ysxq6jvzy-minikube-1.22.0
''
    nativeBuildInputs=''
    /nix/store/2y8p2cx4xabvf1hf810s9zb6cb0bx9mc-docker-compose-1.29.2 /nix/store/sppqwgfpqhjl1lk90gxfdyx2jqxbbfwk-go-1.16.7 /nix/store/hlpk5jjw7f2skknlwh7z2gc0c9qnckl7-go-bindata-3.22.0 /nix/store/gz46hwrdjx9i8gxgkia20ayb2nhyf5vy-grpcurl-1.8.2 /nix/store/dih2gzb715q5k8hw7qjmq0n35ba30pb0-nodejs-16.6.1 /nix/store/g1yan04fzg018134jyz5g36439jd4b3d-postgresql-12.7 /nix/store/zgagnpjcpi2zvimmswrv6pf91svjfjf0-protoc-gen-doc-unstable-2019-04-22 /nix/store/s4lqvzb04xvcdijwq2cancpwvi1807bn-protobuf-3.15.8 /nix/store/svqa4qiz30ddabkfjwx0z69a16h4i14g-go-protobuf-1.5.2 /nix/store/ccd1xjg0p9r23k1i9cpxx9zf7rr36r17-go-protobuf-json-069933b8c8344593ed8905d46d59c6647c886f47 /nix/store/m8n43fdmfnl24d8yh90r9l0xa1w3zvlz-go-tools-35839b7038afa36a6c000733552daa1f5ce1e838 /nix/store/ln0f156f6qcdf15j6gy2mjw263s2clwg-go-mockery-1.1.2 /nix/store/vjx713gmz1qqzllvppnl02f4zpza5gl8-go-changelog-56335215ce3a8676ba7153be7c444daadcb132c7 /nix/store/4mqvyh5q93ja860656bi0q9sg5sqhqs4-doctl-1.63.1 /nix/store/cx42syr9krm4f7hip1za88lr0gmw7y9q-kubectl-1.22.0 /nix/store/2racw0r4a6f1ya6hv7a47w544cgarcjf-autoconf-2.71 /nix/store/jklgf34m49dl7fq5xy3b55szy5zjpq2f-autogen-5.18.16-dev /nix/store/9wgw1bxavq7d4hj3igw8mm4l68vrp5bh-automake-1.16.3 /nix/store/xmdhdglf79q6f5hg9yqbdbzfbrfl9k5v-libpng-apng-1.6.37-dev /nix/store/kxi9r99hgdq1bi7ma135pbn7p3jqlmdk-libtool-2.4.6 /nix/store/gr6hd0mba0217fp8msgmj8sp6a2wn6bh-nasm-2.15.05 /nix/store/3d8z7x0p3fzhjkxdfr3cg6vfkfmqadnd-pkg-config-wrapper-0.29.2 /nix/store/mzpfnpbax7i5b8ipsgf27i7nlmnhpvn3-zlib-1.2.11-dev /nix/store/dbcd4ivx25dqdiq2p95z8q0ysxq6jvzy-minikube-1.22.0
''

[hashicorp-cla]

All committers have signed the CLA.

[mitchellh]

Thanks! I'll give this a shot, but it looks nice.

[mitchellh]

Thanks!

[jonringer]

Anytime :)