Add extension points for data source links and config properties customization.

[emtwo]

This PR places 2 extension points for someone interested in writing an extension that would provide a link for data source documentation.

It also adds the ability to add configuration properties which could be used, for example, to let someone input their desired data source URL from the admin page.

Here is an example of this usage: https://github.com/mozilla/redash-stmo/blob/master/src/redash_stmo/datasource_link.py#L61

[request-info]

We would appreciate it if you could provide us with more info about this issue/pr!

[arikfr]

Do you really use different URLs for the same type of data source?

Wouldn't it be possible for the extension to have a list of URLs that you load based on the data source type and/or name?

[emtwo]

@arikfr Perhaps in most cases the same type of data source will have the same documentation. But, for example, different versions of the same data source type might have different documentation.

Is your concern that you prefer extensions cannot customize config properties? I think it could be useful and generalize to other use cases as well.

[arikfr]

Perhaps in most cases the same type of data source will have the same documentation. But, for example, different versions of the same data source type might have different documentation.

In this case, you can have overrides based on the data source ID/name. It's not very convenient to manage as if it was in the UI, but still manageable considering how (not) often data sources update.

Is your concern that you prefer extensions cannot customize config properties? I think it could be useful and generalize to other use cases as well.

Exactly. Do you have such use cases in mind?

[emtwo]

Is your concern that you prefer extensions cannot customize config properties? I think it could be useful and generalize to other use cases as well.

Exactly. Do you have such use cases in mind?

We've used it before here: mozilla#31 to allow versioned tables to not be visible. I know you've mentioned a couple of times (e.g. mozilla#376 (comment)) your idea to have a better schema browser so that we wouldn't need that feature.

However, there could be additional metadata about a data source that does not always generally apply to every user of Redash. Perhaps for example, we are thinking of having links to sample queries per data source that can serve as documentation to guide a user. These would not be great to have hard-coded since they could change for a variety of reasons (e.g. schema change, adding new examples). But I could also see this being a feature that not everyone needs in Redash.

[emtwo]

@arikfr I think in person you had mentioned a simpler way we can do this. Would you be able to share on this ticket the idea you had in mind? Thanks!

[arikfr]

So my idea was simple:

1. To avoid having to update the configuration schema to add arbitrary data to a data source, let's just have another field on this model to hold the extra options. This field won't have a schema, so can be used by extensions. Also, it won't be encrypted (unlike options post Change: encrypt data source options. 🔓 #2970).

2. Update the data source creation/edit form to have some global options that apply to all data sources. These global options will be stored in this new field.

3. Add extension point to make it possible to add new fields to the global options.

This will be useful for the data source URL option, to store SSH credentials (to support SSH tunnels) or for table filtering options.

WDYT?

[emtwo]

Closing this in favour of #3558