Allow templates in changelogUrl

[mueller-ma]

Tell us more.

As fetching Nuget release notes isn't available yet (see #14128), I created a packageRule to set the changelogUrl for some packages:

{
  "matchDatasources": ["nuget"],
  "matchPackageNames": ["Example.**"],
  "changelogUrl": "https://<private proget server>/feeds/<private feed>/{{ packageName }}/{{ newVersion }}/metadata"
}

However templating isn't allowed in changelogUrl, Can you allow it for that field?

[rarkins]

PR welcome to add this

[neumantm]

I'm contemplating implementing this feature.

I guess a new field changelogUrlTemplate is preferrable over changing the behavior of the existing field.
What do you think?

Also: Any pointers to where in the code the changelogUrl field of the packageRules is applied to the upgrade (BranchUpgradeConfig) would be helpful.

[neumantm]

After some debugging I found that the relevant application of packageRules is in the flattenUpdates function.
I think this is not a sensible place to evaluate a template, so I'm tending to just have the changelogUrlTemplate copied to the BranchUpgradeConfig and evaluate it at some later time.
Where do you think is a good place for evaluating the template?
Maybe in massageUpdateMetadata?

[rarkins]

It's preferred to not add another field. The only thing that's hopefully needed is a template.compile() on this field in massageMetadata