Version upgrades

[davidwheeler123]

I can't seem to compile the project any more because it can't find compatible versions of some of the dependencies

   > Could not resolve org.ajoberstar.grgit:grgit-core:latest.release.
     Required by:
         project :documentation > org.ajoberstar.git-publish:org.ajoberstar.git-publish.gradle.plugin:3.0.0 > org.ajoberstar:gradle-git-publish:3.0.0
      > No matching variant of org.ajoberstar.grgit:grgit-core:5.2.1 was found. The consumer was configured to find a runtime of a library compatible with Java 8, packaged as a jar, and its dependencies declared externally, as well as attribute 'org.gradle.plugin.api-version' with value '7.0.2' but:
          - Variant 'apiElements' capability org.ajoberstar.grgit:grgit-core:5.2.1 declares a library, packaged as a jar, and its dependencies declared externally:
              - Incompatible because this component declares an API of a component compatible with Java 11 and the consumer needed a runtime of a component compatible with Java 8
              - Other compatible attribute:
                  - Doesn't say anything about org.gradle.plugin.api-version (required '7.0.2')
          - Variant 'javadocElements' capability org.ajoberstar.grgit:grgit-core:5.2.1 declares a runtime of a component, and its dependencies declared externally:
              - Incompatible because this component declares documentation and the consumer needed a library
              - Other compatible attributes:
                  - Doesn't say anything about its target Java version (required compatibility with Java 8)
                  - Doesn't say anything about its elements (required them packaged as a jar)
                  - Doesn't say anything about org.gradle.plugin.api-version (required '7.0.2')
          - Variant 'runtimeElements' capability org.ajoberstar.grgit:grgit-core:5.2.1 declares a runtime of a library, packaged as a jar, and its dependencies declared externally:
              - Incompatible because this component declares a component compatible with Java 11 and the consumer needed a component compatible with Java 8
              - Other compatible attribute:
                  - Doesn't say anything about org.gradle.plugin.api-version (required '7.0.2')
          - Variant 'sourcesElements' capability org.ajoberstar.grgit:grgit-core:5.2.1 declares a runtime of a component, and its dependencies declared externally:
              - Incompatible because this component declares documentation and the consumer needed a library
              - Other compatible attributes:
                  - Doesn't say anything about its target Java version (required compatibility with Java 8)
                  - Doesn't say anything about its elements (required them packaged as a jar)
                  - Doesn't say anything about org.gradle.plugin.api-version (required '7.0.2')

Which makes me wonder whether it's time to upgrade some of our expected versions. I can put a PR together, but I'm interested to know what versions you'd like - especially for target java version

1. Java 1.8 -> Java 11 (or 17 - the oldest oracle supported LTE version?)
2. Gradle 7.0.0 -> 8.4 (latest)
3. Kotlin 1.4 -> 1.9.10 (latest)

Any reason everything else shouldn't go to latest? (I won't put that all in 1 PR)

[davidwheeler123]

Attempt in #578