Search provider for external apps

[ThreeDeeJay]

Follow-up from #920 (comment)

Is your feature request related to a problem? Please describe.

It would be nice to be able to search articles using external apps such as voice assistants by making the app searchable.

Describe the solution you'd like

Adding Kiwix as a search provider so that we could add it as a custom command for offline voice assistants like Saiy/Utter in Search mode (just show matches/results) and maybe also Search & Play mode (go directly to the first/closest match and/or immediately start reading aloud using Text-to-Speech, if enabled, for extra convenience/speed which may even work when the display is off or device is locked)

Describe alternatives you've considered

Searching manually via the Search button in the app.

Additional context

Examples of apps with search providers available in Utter:

For instance, we can add a voice command in Utter to search for a local music file by saying play TITLE and it'll show the results matching TITLE. And if we use the Search & Play mode, it'll immediately start playing the first file that matches TITLE.
So I'm thinking of something like that, but for articles in Kiwix.

[kelson42]

@MohitMaliDeveloper Same as #30?