[1.x] Expose the EnvSetting class

[Artem-Semenov-dev]

The EnvSetting class is a tool that allows configuring the value that may differ across environment types. Previously it was an internal tool, but now it is available for all Spine projects.
Usage example:

    EnvSetting<UserReader> setting = new EnvSetting<>();
    setting.use(projectsUserReader(), Production.class)
           .use(localUserReader(), Local.class)
           .use(testsUserReader(), Tests.class);
    
    // ...

    // The instance is returned according to the current `Environment` type.
    final UserReader reader = setting.value(); 

This changeset includes the following changes in the EnvSetting:

• introduced method chaining for a more fluent and convenient API (as shown in the example);
• added a new method that allows retrieval of the stored value for the current environment type of the application;
• made the API thread-safe, allowing concurrent read operations while ensuring exclusive access for write operations to maintain data integrity.

[armiol]

@Artem-Semenov-dev Mostly LGTM. Please see my comments.

[armiol]

I am not sure we want that, I would just ignore.

If you still think we need to re-throw, please have a method-level comment explaining the behaviour.

[armiol]

Maybe we could return this? For call chaining, that is.

I am asking since the example from the PR description is a bit mouthful. I think I would look better like this:

    EnvSetting<UserReader> setting = new EnvSetting<>();
    setting.use(projectsUserReader(), Production.class)
           .use(localUserReader(), Local.class)
           .use(testsUserReader(), Tests.class);

[armiol]

@Artem-Semenov-dev

   UserReader currentUserReader = setting.use(projectsUserReader(), Production.class)
                                          .use(localUserReader(), Local.class)
                                          .use(testsUserReader(), Tests.class)
                                          .value();

This should be an illustration of some real-world usage. In which (on Earth) scenario, one would call .value() right after .use()?

[armiol]

@Artem-Semenov-dev LGTM. However, please change the PR description according to my comment.

[armiol]

@Artem-Semenov-dev please update the README.md. There is a version number that you've changed.