[SQLite] add methods to operate on keyservers table

Summary:

1. Representation of data row.
2. Methods to modify the table.
3. Emscripten bindings.

Note: This could heavily conflict with @marcin's work on deprecating sqlite_orm - we will coordinate to make this smooth and avoid blocking each other.

Depends on D10774

Test Plan: Calling those methods from JS and making sure it works.

Reviewers: inka, marcin

Reviewed By: marcin

Subscribers: ashoat, tomek, marcin

Differential Revision: https://phab.comm.dev/D10775