Expand acceptable datasource regex on dockerfileVersions preset custom manager

[bpfoster]

Tell us more.

The dockerfileVersions custom manager preset currently has a very restrictive pattern for the datasource parameter:

datasource=(?<datasource>[a-z-.]+?)

With the introduction of custom datasources, it would be nice if this were relaxed a little bit. Renovate documentation for custom datasources shows examples utilizing _ in the name, but this won't match here.

I would propose something perhaps like:

datasource=(?<datasource>[a-zA-Z0-9-._]+?)

This would allow a custom datasource with a name like alpine_3.21_main which would be very helpful for my use cases.

I see that other custom managers in that file use the same regex for the datasource, so maybe the scope of this is not limited to just dockerfileVersions, and may want to be applied to other managers.

[viceice]

PR welcome