Adds godot symlink to OS' PATH, auto-detect default SHELL on UNIX systems

[edassis]

Hi,

I have been messing around with godotenv for some weeks now, and I really liked it. I'm mainly using it to manage my godot installations.

My major complaint is that I can't call the new godot install through the terminal easily. The installation process gives me the GODOT env-var, but not exports the symlink in the system PATH nor provides some guidance of how to do it.

This PR addresses this and another improvements:

Mainly touches in godot env setup and godot install commands.

• Godot binary path now is ../godotenv/godot/bin/godot instead of ../godotenv/godot/bin;

  GODOT env was updated accordingly.

• Exports godotenv's godot bin folder in user's PATH on all OSes;

  Now it's possible to call godot by just typing it on the terminal.

• Env var changes on Windows occur on USER environment now, instead of SYSTEM;

  This change tries to make env-var setup more concise across OSes and minimizes the need for an elevated cmd shell. SystemEnvironmentVariableClient class was renamed to EnvironmentVariableClient. Some methods name has been changed:
  SetEnv → SetUserEnv
GetEnv → GetUserEnv
  References in documentation citing "system environment ..." was updated to "user environment ...".

• FileClient.AddLinesToFileIfNotPresent() now writes to the end of the file;

  This way, new var exports have priority over older ones.

• Tries to detect the user's default shell automatic;

  People changes the default shell on Linux frequently. So this tries to make a more sensible decision.
  To keep things simple and not break godotenv's shell commands, it is assumed that the user's shell is POSIX-compliant (bash, zsh, sh).
  Two new functions have been added in EnvironmentVariableClient.GetDefaultShell(), and
  EnvironmentVariableClient.IsShellSupported().
  I think it would be great to call these functions in the program initialization (before running any command) to detect the user's default shell and validate it. But I didn't figure out a good way to do it.
  This should resolve the issue [FEATURE] Support for other shells #32.

• Tests.
  Added some tests for EnvironmentVariableClient and GodotRepository.

I did manual testing on Mac M1 13.6.1 (zsh), Ubuntu 22 (zsh and bash) and Windows 11 (PowerShell).

Let me know what you guys think. In case necessary, I can remove or split the changes in another PR.

---

EnvironmentVariableClient's SetUserEnv() and AppendToUserEnv() are declared as async function, but their routines are totally synchronous at the moment. So I think we can change their definitions.

And, the other way around, GetUserEnv() and GetDefaultShell() are synchronous but could be made asynchronous.

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Some pictures:

• GODOT env:
  

• PATH updated:
  

• Calling from terminal:
  

• User's shell not supported behavior:
  

[definitelyokay]

Thanks for taking a look and working on all this.

Let me know when this is ready for a closer look.

[definitelyokay]

Let me know if this is ready and I'll take a closer look. (I keep accidentally pressing the "ready for review" button for some reason)

[edassis]

I think this PR is in good shape for review now! Let me know what you think and if I need to change something.

[definitelyokay]

Thank you for all your hard work, things are looking great! I left a few comments here and there, nothing major.

[edassis]

@definitelyokay, I'm not seeing any pending comments or conversation for me to resolve. Maybe I'm doing something wrong? I don't know 😅.

[definitelyokay]

ah, forgot to actually submit my review 😆

[definitelyokay]

Thank you so much for all your hard work on this. Just the one little comment, it's looking really good!

[edassis]

I'm making a last round of tests.

[edassis]

Seems to be working as expected :).