chore(opa): Update major/minor versions for 26.11.0

Part of https://github.com/stackabletech/docker-images/issues/1641.

• Add: 1.20.2 (supported)
• Deprecate: 1.16.2
• Remove: 1.12.3

[!TIP]
Please add to the Stackable Engineering project.

Update tasks

• Update boil-config.toml to reflect the agreed upon versions in the spreadsheet (including the removal of old versions).
• Update other dependencies if applicable (eg: golang-version, etc).
• Check the corresponding operator (getting_started / kuttl / supported-versions) for usage of the versions.
• Check other operators (getting_started / kuttl / supported-versions) for usage of the versions. Add the PR(s) to the list below.
• Update the version in demos. Add the PR(s) to the list below.

Related Pull Requests

[!TIP]
Delete any items that do not apply so that all applicable items can be checked.
For example, if you add release notes to the documentation repository, you do not need the latter two criteria.

• Link to the docker-images PR (product update)
• Link to the operator PR (getting_started / kuttl / supported-versions)
• Link to any other operator PRs (getting_started / kuttl)
• Link to demo PR (raise against the main branch)
• Link to the Release Notes PR in the documentation repo (if not a comment below)

Acceptance

[!TIP]
This list should be completed by the assignee(s), once respective PRs have been merged. Once all items have been
checked, the issue can be moved into Development: Done.

• Can build image (either locally, or in CI)
• All kuttl tests pass (either locally, or in CI)
• Release notes added to documentation and linked as a PR above
• Release notes written in a comment below
• Applicable release-note label added to this issue

# Where x.y.z is the new version added in this PR
boil build opa=x.y.z --strip-architecture --load

kind load docker-image oci.stackable.tech/sdp/opa:x.y.z-stackable0.0.0-dev

# Change directory into the opa-operator repository and update the
# product version in tests/test-definition.yaml
./scripts/run-tests --test-suite smoke-latest # or similar

Please consider updating this template if these instructions are wrong, or
could be made clearer.

Start with boil-config.toml and the agreed versions in the spreadsheet, then search the corresponding operator's getting_started, kuttl, and supported-versions files plus other operators and demos for old versions. Use the listed boil build command and operator smoke tests to verify the image and related changes; done means the update tasks and acceptance checklist are complete, including release notes.