Added more breaking changes to the 9.0 docs

[l-trotta]

Java 8 to 17 target + RestClient optional dependency breaking changes + known issues

[swallez]

NoClassDefFoundError is very generic, we should be more precise so that users can know here if this applies, like "NoClassDefFoundError(org/apache/commons/logging/LogFactory)"

[github-actions]

The backport to 9.0 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-9.0 9.0
# Navigate to the new working tree
cd .worktrees/backport-9.0
# Create a new branch
git switch --create backport-1004-to-9.0
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 c18017112bd237de29264404ba2930e01cae7f5f
# Push it to GitHub
git push --set-upstream origin backport-1004-to-9.0
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-9.0

Then, create a pull request where the base branch is 9.0 and the compare/head branch is backport-1004-to-9.0.