Ability to add custom external links for a database in the UI

[kobzonega]

Currently, the UI automatically provides built-in links to Monitoring and Logs for each database.

We need to support additional configurable external links per database—for example:

slo_logs: a link to Monium showing SLO ydb_availability logs specific to the database
cores: a link to "Three Crusts" to view crash dumps related to the database

This feature should be designed to support additional links in the future without requiring UI changes—ideally by defining associated inside configuration via database.