Support custom tag naming

[davidmartos96]

Hello!
After trying to use this package on our project, we found ourselves with a limitation when using the diff and tag template URLs.
On our Flutter app releases, we use a tag prefix to trigger CI/CD pipelines. So a git tag "v1.0.0" would actually release and a tag "1.0.0" wouldn't.
What this PR does is add an extra config option "link_template/version", which is a template for the version used in link templates (tag or diff). In this case the template could be: "v%value%"

I look forward to your thoughts on this.

[f3ath]

Thanks for the PR. I get the point and think it'd be a nice feature. Just for the sake of consistency, how about using the templating mechanism we already have? I mean a new class like

import 'package:cider/src/template/template.dart';

final class Version extends Template {
  const Version(super.template);

  String render(Object version) =>
      template.replaceAll('%version%', version.toString());
}

Let's call it version instead of tag_prefix and let the default template value be just %version%?
So that the config will look like

cider:
  link_template:
    diff: https://github.com/example/project/compare/%from%...%to%
    tag: https://github.com/example/project/releases/tag/%tag%
    version: v%version%

What do you think?

[davidmartos96]

@f3ath Didn't think of that. It's a great idea. I have pushed the alternative design

[f3ath]

Thank you!