Breaking refactor to further unify sidebar and navigation API

[caendesilva]

This PR will breakingly remove the DocumentationPage::$category property and use HydePage::$navigation['group]' instead. This will require existing documentation pages to update their front matter. However, in the end this will become more consistent and match #495.

In addition and similar to the reasons in the original PR; further arguments for this change is that the naming is also inconsistent when it comes to sidebar categories and groups, for example the important DocumentationSidebar.php uses the term group exclusively, yet the front matter property is named category. Same in the NavItem class and many more places I'm sure I'll discover as I refactor this. Even the Blade views use the term groups.

[codecov]

Codecov Report

Merging #498 (a3f2022) into master (6d65654) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #498   +/-   ##
=========================================
  Coverage     99.95%   99.95%           
- Complexity      927      929    +2     
=========================================
  Files           107      108    +1     
  Lines          2284     2300   +16     
=========================================
+ Hits           2283     2299   +16     
  Misses            1        1           

Impacted Files	Coverage Δ
...rk/src/Concerns/Internal/ConstructsPageSchemas.php	100.00% <ø> (ø)
...s/framework/src/Models/Pages/DocumentationPage.php	100.00% <ø> (ø)
packages/framework/src/Concerns/HydePage.php	100.00% <100.00%> (ø)
.../src/Concerns/Internal/GeneratesNavigationData.php	100.00% <100.00%> (ø)
...ckages/framework/src/Models/Navigation/NavItem.php	100.00% <100.00%> (ø)
packages/framework/src/Models/NavigationData.php	100.00% <100.00%> (ø)

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