New DNS settings

[antonsoroko]

Description

New settings:
"DNS over HTTPS Server"
"Custom DNS over HTTPS Server"
"Use OpenNIC DNS Servers"
"Use OpenNIC DNS only for OpenNIC zones"

also see elgatito/elementum#175

Related Issue

for #1170

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Translation

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[antonsoroko]

@elgatito ready for review.