Make environment builds more robust w.r.t. .orchest being git ignored #1494

Describe the problem this improvement solves
Orchest expects the .orchest/environments directory to be versioned (or, at least, to not be .gitignore'd). This is because an environment build will take a snapshot of the project, and said snapshot will exclude files and directories according to the .gitignore file. However, some users would like to not version any content of the .orchest directory.

Describe the solution you'd like
The build should work regardless of the .orchest directory being in the snapshot or not. Making the build read the environment properties and setup script prior to the snapshot should be feasible. Note: the PR fixing this should include some changes to docs/source/fundamentals/environments.md to remove the notion that .orchest/environments shouldn't be git ignored (i.e. revert 02c2fa4.