[PSR-19] Proposal for adding generated tag

[ezimuel]

This PR is a proposal to add a @generated tag in PSR-19. This tag indicates that the code has been generated using an automation script. This is quite common in projects where the code is generated from a specification (e.g. OpenAPI). This tag should be used to warn to do not change the code, since the change will be overwritten by the
automation script.

For instance, you can mark a PHP class that has been generated using a script, as follows:

/**
 * Index a document in Elasticsearch
 * 
 * @generated class generated using bin/script.php, please DO NOT EDIT!
 * 
 * @version 7.14.0 Elasticsearch
 */
class Index
{
    <...>
}

The comment in the @generated class can useful to give information about the automation script. In this way people can contribute to the automation script rather than doing the mistake of chaning the code manually.
Moreover, the @generated tag can be used to automate alert (e.g. using Github Action) for manual change in the code.

[ezimuel]

Thanks @PowerKiKi for your suggestions.

[ezimuel]

Suggestions applied

[ezimuel]

@ashnazg may you review this PR? Let me know if you have time, thanks.

[ashnazg]

Looks ok.

[ezimuel]

Thanks @ashnazg