update to sbt-typelevel 0.6 with Laika 1.0

[jenshalm]

Hello out there. I picked doodle as a sample project for a test migration to Laika 1.0 as you do a few things other projects don't (writing your own directives, not using the Helium theme) which makes it a good additional test case. I'm turning this into a PR since I did the work already anyway and you may want to migrate at some point, too.

Laika 1.x is intended to offer long-term API stability, so it's hopefully the last occasion for a long time such a migration step is necessary. Don't get misled by the version numbers, sbt-typelevel and Laika both did a milestone release which turned into an actual RC over time (since no issues could be found so far). We expect little to no changes for the final releases of both. Feel free to either merge this now or park it until the finals are out (in about 2 weeks aprox.) in which case I can update the PR if you want.

Summary of changes:

• Tweaks a lot of imports since there is a new package structure for Laika 1, see the PR for details.
• Tweaks the syntax for LinkConfig which, like many other config types, is no longer a case class so that it can evolve in a binary compatible way.
• Tweaks your custom template which used the linkCSS and linkJS directives which are no longer available (they have richer configuration now and had to move to the Helium theme for this purpose which you do not use). Your use case is simple enough that the use of the @:target directive is sufficient (it ensures the link is always valid relative to the rendered document)

The build will most likely be red since most of your recent builds on main are red, but I did a few local tests and compared the results to your hosted site (both visually and by comparing HTML sources) and could not easily spot a difference.

[noelwelsh]

Thanks!