[Documentation:Developer] Update php route info

[roye2]

Why is this Change Important & Necessary?

The documentation concerning Routes was outdated. The old syntax of @Route(...) is deprecated and in fact will no longer work with the recent update to the Route object we include from Symfony in PR #12935.

New Additions

Instances of @Route(...) have been replaced with #[Route(...)] to match what will be expected from developers when writing PHP code.

Screenshots

Before

1. Controller page:

2. Excerpt from Router page:

3. Excerpt from Routes and Responses page:

After

1. Updated Controller page:

2. Updated Router page:

3. Updated Routes and Responses page:

Other information

Unfortunately, the markdown renderer thinks the #[Route(...)] syntax is a comment due to the leading #. If at some point GitHub pages updates their markdown renderer to allow for PHP 8 syntax highlighting then the Routes will appear correctly as uncommented.
Example of how it is now:

Here is how it actually looks in the code:

Notice how the routes are not italicized.

This is not really a big deal but it kind of annoys me that the routes look like they are comments. However, I think that is better than rendering these code blocks as plain text or a different language than php (both of which would make the route appear 'correctly').

Also, the example given of UserController on the Controller / View pages is code that no longer exists in the submitty codebase. It is still a good example of how to write our php code but at some point we should probably update the example to use real code.