docs(guide/Filters): adding a a clear link to angular built-in filters

[lirantal]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Documentation update for the online guide of angularjs

What is the current behavior? (You can also link to an open issue here)
In the Filter guide on the angularjs docs, there are a few examples of filters but no direct link to see a list of the supported built-in filters

What is the new behavior (if this is a feature change)?
Making it clear to the reader where to find a list of supported built-in filters: https://docs.angularjs.org/api/ng/filter

Does this PR introduce a breaking change?
No, it's a documentation update.

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#commit-message-format
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

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[lirantal]

I signed it!

[googlebot]

CLAs look good, thanks!

[googlebot]

CLAs look good, thanks!

[gkalpak]

Tweaked it a bit and landed. Thx!