* remove unused datasource pages
* move useDataSourceSettingsNav from datasources to connections
without any modification in the code yet
The reason for this is that its only usage is in this file, so we are
going to merge it with the other useDataSourceSettingsNav hook in the
next commit.
* merge two useDataSourceSettingsNav's
and rename consts and remove duplicated calls
* simplify useDataSourceSettingsNav
rename "Your data source" to "Data source" page
This page was meant to be named "Data source" in the previous PR [0].
I just made a mistake by naming it wrongly.
[0]: https://github.com/grafana/grafana/pull/66813/files
* fix: use the correct URL for editing datasource dashboards
* feat: show the Datasource/Dashboards page under Connections as well
* refactor: remove unnecessary `useNavModel()` utility
* feat: add a utility for creating the nav-model for DS settings tabs
* refactor: use nav-model crating utility in Edit Datasource
