Add backdrop-filter to our popup overlay background

[fmontes]

Is your feature request related to a problem? Please describe. We want to make the app looks more "appy" (Jason's words) so for the overlay of the dialogs we want to add:

    backdrop-filter: blur(5px);

Describe the solution you'd like We need to add this for primeng dialog and our custom dot-dialog component.

[alfredo-dotcms]

Note to QA: this can be checked comparing demo with the effect on the background blur of this img

[alfredo-dotcms]

PRs: https://github.com/dotCMS/core-web/pull/1870/files https://github.com/dotCMS/core/pull/21665/files

[nollymar]

Internal QA: Passed

[bryanboza]

Fixed, tested on release-21.03 // Docker // FF