Feature: Finish Implementing Custom Search Engine

[o0-o]

Preflight Checklist

• [X] I have read the Contributing Guidelines for this project.
• [X] I agree to follow the Code of Conduct that this project adheres to.
• [X] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Problem Description

Custom search engines (such as private SearXNG instances) are not configurable.

Proposed Solution

Other browsers such as Firefox and Brave allow the user to configure custom search engines.

Alternatives Considered

N/A?

Additional Information

This is continuation of #240 which was closed while only being partially implemented.

See: https://github.com/ferdium/ferdium-app/issues/240#issuecomment-1847080814

[trymeouteh]

Would like to see this feature as well.

When adding a search engine, you will be asked for the following information...

• Name
• URL (With %s) added in it which will be replaced with the search query