Add Gradle wrapper infrastructure

[sbesson]

As I am occasionally (but not daily) building the OMERO server components, I get periodically tripped by the (undocumented) Gradle 6.x requirement for building these projects. When either Gradle is not installed or a more recent version of Gradle is installed globally, the build will fail spectacularly.

My workaround is to copy the Gradle wrapper infrastructure from another project and execute ./gradlew build.

This commit opens the discussion about adding these wrappers to the source code repository. With this change, someone should be able to clone this repository and execute

./gradlew build

This wrapper infrastructure should not affect the existing build logic using a system Gradle and should be compatible with both the GitHub Actions and OME Jenkins CI workflows. Two additional considerations:

• given the separation of the OMERO repositories, this decision affects all ome/omero-* repositories
• a wrapper was initially added during the decoupling work (b6957e1e) but was removed in https://github.com/ome/omero-blitz/pull/13 and specifically c295ce2d715245f0387292b4a9e4becba823723a although the rationale is not discussed in the commit or PR The rationale for not adding these wrappers dates from the early days of the components migration to Gradle.
• in the context of a future upgrade of Gradle to 7.x/8.x (I could not find a reference issue), this might be an alternative strategy to consider especially as CI would need to be updated

[jburel]

No objection but we may want to propagate that to other repositories e.g. omero-model etc. The build strategy will also need to be reviewed. Omitting this PR from the release for now

[sbesson]

Moving back to draft in the absence of a consensus/driver for the time being.

[sbesson]

Discussed today at the weekly infrastructure meeting with @jburel @khaledk2 @pwalczysko. There is currently no active plan to move to the Gradle wrapper infrastructure everywhere so I am closing this draft PR and we can come back to it if there is a consensus.

However, it is quite clear there is a lack of documentation for developers interested in building the OMERO.server components. @khaledk2 just came across the issue that all these repositories require Gradle < 7 (which was one of the motivations of this PR). As discussed today, an immediate step is to update these repositories and capture the build requirements either via the readme and/or the GitHub workflows.