Proposal project structure

[marcofranssen]

I would love to cleanup some more scripting e.g. Makefile.

For that I would also like to put a bit more convention into the directory structure and clean this up a bit as well, to simplify Dockerfiles etc.

Main idea is to move cmd, pkg, api one folder up.
Then within the cmd folder we name those to match the intended binary names, this allows massive simplification in Makefile + is a pretty common convention in Go projects. Also renaming those files to main.go to make it more clear these are executable entrypoints.

For the tornjak-frontend folder I would suggest to rename the folder to just frontend as the tornjak part is implicitly already there in the repo name.

Happy to send this as a PR on top of #275 to further simplify make targets as well continue cleanup of Dockerfiles. Doing that cleanup will allow me as well to implement the support for multi-architecture images like I did for all the other spiffe projects.

Please let me know if I should invest some time on these improvements?

See below an example of what I intend to do, left a whole bunch of files and folders for brevity.

.
├── LICENSE
├── Makefile
├── api
│   ├── agent
│   │   ├── api.go
│   │   ├── server.go
│   │   └── types.go
│   └── manager
│       ├── api.go
│       └── server.go
├── cmd
│   ├── tornjak-backend
│   │   └── main.go
│   └── tornjak-manager
│       └── main.go
├── config.conf
├── frontend
│   ├── axios.d.ts
│   ├── babel.config.json
│   ├── jest.config.js
│   ├── package-lock.json
│   ├── package.json
│   ├── public
│   │   ├── favicon.ico
│   │   ├── …
│   │   └── robots.txt
│   ├── src
│   │   ├── App.css
│   │   ├── …
│   │   └── tables
│   ├── tsconfig.json
│   └── webpack.config.js
├── go.mod
├── go.sum
├── pkg
│   ├── agent
│   └── manager
├── run_backend.sh
├── run_tornjak.sh
└── version.txt

43 directories, 126 files