support sbt plugins

[pjfanning]

I used this tool to check https://github.com/apache/incubator-pekko-sbt-paradox

And got

[info] # `pekko-theme-paradox_2.12-1.0.1-RC2.buildinfo`: NOT OK
[info] 
[info] - pekko-theme-paradox-1.0.1-RC2.pom: Missing in theirs but present in ours
[info] - pekko-theme-paradox-1.0.1-RC2.jar: Missing in theirs but present in ours
[info] 
model contains 7 documentable templates
[info] Main Scala API documentation successful.
[info] Downloading certification from [https://repository.apache.org/content/groups/staging/org/apache/pekko/pekko-sbt-paradox_2.12/1.0.1-RC2/pekko-sbt-paradox_2.12-1.0.1-RC2.buildinfo]
[info] # `pekko-sbt-paradox_2.12-1.0.1-RC2.buildinfo`: NOT OK
[info] 
[info] - pekko-sbt-paradox-1.0.1-RC2.jar: Missing in theirs but present in ours
[info] - pekko-sbt-paradox-1.0.1-RC2.pom: Missing in theirs but present in ours
[info] - pekko-sbt-paradox_2.12_1.0-1.0.1-RC2.jar: Missing in theirs but present in ours
[info] - pekko-sbt-paradox_2.12_1.0-1.0.1-RC2.pom: Missing in theirs but present in ours

It seems like this tool may not support sbt plugins

[raboof]

plugins are supported better on the main branch now, but pekko-sbt-paradox (and sbt-reproducible-builds itself) still runs into the trouble described in #309