Allow to add any route

[andresmgot]

We want to list custom resources in the sql datasource (like regions for AWS plugins). Since these routes/resources are not generic, this PR adds the possibility to set any custom route. More context here.

[sunker]

Nice! One potential problem is that the custom routes could override the completion routes. The only solution that I can think of would be to mount each custom route under a predefined prefix path, like custom/regions. But that also makes the api a bit harder to understand for the user. Thoughts?

[andresmgot]

One potential problem is that the custom routes could override the completion routes

I have added a check for that: https://github.com/grafana/sqlds/pull/29/files#diff-651d914d00ae86a3bf860ac5084dbbfa633aa6c35294802ee7fdf0cc761cad4dR109-R111 WDYT?

[sunker]

I have added a check for that: https://github.com/grafana/sqlds/pull/29/files#diff-651d914d00ae86a3bf860ac5084dbbfa633aa6c35294802ee7fdf0cc761cad4dR109-R111 WDYT?

I missed that, nice!