integrate spotless to prettify the generated code

[pahjbo]

As a slightly unfortunate side effect of the code being generated via XSLT it is sometimes rather difficult to ensure that it is nicely formatted - the proposal is to use spotless https://github.com/diffplug/spotless to unify the format of the generated code. The gradle spotless plugin should be automatically included and configured by the VO-DML plugin

[pahjbo]

this is done "longhand" in the sample project gradle build

vo-dml/tools/gradletooling/sample/build.gradle.kts

Line 63 in ff522ff

//TODO integrate this into the main vodml plugin https://github.com/ivoa/vo-dml/issues/53