CP-13581 linux-pkg: skip rebuilding windows-connector when its cached artifact is already up to date - #407

The windows-connector package is rebuilt from scratch on every linux-pkg pipeline run, even when its source hasn't changed since the last successful build. Unlike other linux-pkg packages, windows-connector's build toolchain (nsis/mono/mingw-w64) lives outside our own source and can drift independently of any windows-connector code change — rebuilding on every unrelated trigger risks silently shipping a different toolchain combination without anyone deciding to re-certify it. This also masks the underlying dependency-drift bug (see dlpx-app-gate#4648) — the failure only surfaces when a buildserver's live apt mirror happens to have moved out of sync with the previously-pinned Artifactory dependency zips.

Add a new project.ext.connectorDebVersion in appliance/host/windows/build.gradle, bumped manually whenever connector source changes (independent of connectorVersion, which is bumped once per release regardless of whether the connector itself changed). Change config.sh's build() so the package is only rebuilt when that version doesn't have a matching artifact yet, reusing existing linux-pkg infrastructure rather than adding anything new:

• Look up windows-connector's own current latest post-push artifact via get_package_dependency_s3_url — the same lookup every linux-pkg package already uses to fetch its own build dependencies.
• If windows-connector_<connectorDebVersion>_all.deb already exists there, skip the build entirely and leave a .build_skipped marker file in the artifacts directory instead of trying to reuse/republish anything itself — devops-gate#4772 teaches the shared pipeline to recognize that marker, report a normal Jenkins NOT_BUILT result, and (for the multi-package orchestrator) resolve the existing artifact directly for downstream consumers.
• Otherwise, build it (gradlew build + createDebPackage) as before. No explicit upload is needed — the shared post-push Publish stage already syncs the result to S3 and updates latest for us, exactly like every other package, when the build wasn't skipped.
• The existence check fails soft: if the previous artifact (or its latest pointer) is ever missing for any reason, it just falls through to a normal build and republishes, rather than aborting.

This supersedes two earlier approaches tried in this PR: a bespoke release-de-images/windows-connector-cache/ S3 path, and (after that) writing a BUILD_STATUS file for a custom Slack notification line. Both were abandoned in favor of reusing existing latest-artifact infrastructure and Jenkins' own supported SUCCESS/NOT_BUILT result codes — no new S3 location, no new status plumbing.

Personal Jenkins controller testing: ops-jenkins's shared generate-jobs seed job embeds each job's pipeline script from a fixed branch at seed time rather than reading it fresh per build, so exercising in-flight devops-gate changes (like devops-gate#4772) required a personal developer Jenkins controller pinned to that PR's branch (JenkinsManager configure -j ops -g devops-gate=<branch>,linux-pkg). Two runs there cover both sides of this change:

• Seed job that built the job definitions from the branch under test: generate-jobs #1
• Build job that used those generated definitions to exercise this PR's cache-hit/skip path against a real windows-connector build: build-package/custom #2 — .build_skipped marker correctly detected, Finished: NOT_BUILT.

This PR depends on devops-gate#4772 to be safe to land — without it, a skipped build's .build_skipped marker is never checked, and the shared pipeline falls through to Publish with nothing to publish. Related, separately-tracked follow-ups:

• dlpx-app-gate#4648: drop the pinned mono/mingw/nsis Artifactory zip, install those tools live from apt.
• A git review pre-commit check (and/or CI check) in dlpx-app-gate requiring connectorDebVersion to be bumped whenever appliance/server/connector or appliance/host/windows source changes — without it, a merged windows-connector fix that forgets the version bump would be silently served from cache instead of shipping.

Tracked under epic CP-13579, alongside CP-13582 (app-gate).