feat(router): Add `Route.metatags` and `Route.pageDescription` to Route definitions

### Which @angular/* package(s) are relevant/releated to the feature request?

@angular/router

### Description

As a follow up to #7630 it would be nice to also add both `metatags` and `pageDescription` to the router's definition API in order to streamline how developers define routes.

We can also explore what other data is commonly defined and managed with custom strategies in the `Route.data` property to see how else we could simplify Route definitions especially for new developers.

### Proposed solution

```
const routes : Routes = {
path: '',
title: 'Angular Home Page',
metatags: ['home', 'angular'],
pageDescription: 'Home page for Angular documentation',
children: [
{path: 'about', title: 'About Angular', metatags: ['info', 'about'], pageDescription: 'About page for Angular documentation',},
{path: 'docs/:param', title: TitleResolver, metatags: MetatagResolver, pageDescription: PageDescriptionResolver}
]
};
```

### Alternatives considered

Currently this is individually managed and already possible with the `Route.data` additional attributes, which works but is more work for the developer and does not enforce best practices.

Start with the @angular/router Route definition API and its existing Route.data attributes, then review follow-up #7630 and the discussion for the intended scope. Done requires a maintainer-approved design for metatags and pageDescription, including resolver forms, plus agreement on whether additional Route data should be included.

Written by the indexing model from the issue text.