[Tooling] Update and Modernize CI pipeline

[AliSoftware]

What does it do?

• Start using our typical shared-pipeline-vars for DRY-ing common values used in our pipeline file (instead of relying on YAML anchors)
• Update the IMAGE_ID Xcode VM used from the very old 16.1 to the latest 26.1.1 image
• Update ci-toolkit and docker Buildkite plugins to more recent version

Checklist before requesting a review

• Run bundle exec rubocop to test for code style violations and recommendations.
• Add Unit Tests (aka specs/*_spec.rb) if applicable.
• Run bundle exec rspec to run the whole test suite and ensure all your tests pass.
• Make sure you added an entry in the CHANGELOG.md file to describe your changes under the appropriate existing ### subsection of the existing ## Trunk section.
• If applicable, add an entry in the MIGRATION.md file to describe how the changes will affect the migration from the previous major version and what the clients will need to change and consider.

[mokagio]

Suggested change

	export RUBY_VERSION="3.2.2"
	export RUBY_VERSION="$(cat .ruby-version)"

That's how we do it in other repos that have .xcode-version, but thinking about it I don't like how it assumes that the script runs (is sourced) from the project's root. Should use BASH_SOURCE[0] appropriately (which I don't remember off the top of my head).

[mokagio]

LLM to the rescue:

Suggested change

	export RUBY_VERSION="3.2.2"
	SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
	export RUBY_VERSION="$(cat "$SCRIPT_DIR/.ruby-version")"

[mokagio]

@copilot open a PR to implement the suggestion I left above, thanks.

[mokagio]

🤔 I think Copilot didn't acknowledge this or do any other work because I commented after merging and the branch was delete as a result of the PR being merged.

[mokagio]

Assigned #679 to Copilot to see what it does.

[mokagio]

Nice to shake the rust off this one.