ci: use .java-version and prepare to use VM with installed tools in BK

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What does this PR do?

• Enable .java-version - that contains the current major java version
• Enable dry-run in the release/snapshot by default.
• Fallback to install java in Buildkite if the JAVA_HOME is not in the Buildkite runner - a follow-up to use a VM with the installed tools

Why

• Stability and reliability.
• Faster builds.

Follow-up

• Use the VMs with the tools in Buildkite

Test

Triggering manually against this particular feature branch (for such, I use the snapshot one):

• Snapshot build in Buildkite
• Release build in Buildkite

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run docs

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run docs build

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run docs-build rebuild

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run docs-build rebuild

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run docs-build