Add pluggable TSS backend support to smoke test infrastructure

[cnewkirk]

Summary

• Add INTEGRATION strategy to TimeSeriesStrategy enum, enabling smoke tests to run against pluggable TSS backends (Cortex TSS plugin with Prometheus/Thanos)
• Add ThanosReceiveContainer and ThanosQueryContainer for distributed Thanos backend testing
• Add PrometheusContainer as a standalone building block (not wired into default INTEGRATION stack)
• Add TimeSeriesValidationUtils with strategy-agnostic validation methods for resource trees, measurements, metadata, and all aggregation types
• Add CortexTestUtils.resolveKarFile() shared utility for KAR file resolution
• Wire OpenNMSStack and OpenNMSContainer for INTEGRATION strategy (cortex.cfg overlay, opennms.properties, features boot)
• Expand CortexTssPluginIT to 26 test methods covering plugin lifecycle, write/read path, meta tags, metric sanitization, label ordering, resource discovery, two-phase discovery, and data consistency
• Update CortexTssTimeseriesPluginIT to use shared CortexTestUtils
• Add smoke-test/README.md with INTEGRATION section, Mermaid architecture diagram, prerequisites, and validation utilities

Companion PR

• Plugin changes: Use label values API for efficient wildcard resource discovery opennms-cortex-tss-plugin#1

KAR File Resolution

Tests use CortexTestUtils.resolveKarFile() to find the Cortex TSS plugin KAR:

• -Dcortex.kar=/path/to/plugin.kar — explicit path (throws if path invalid)
• -Dorg.opennms.dev.m2=$HOME/.m2/repository — bind-mount Maven repo for Karaf resolution

Test plan

• Compiles clean with Java 17 and -Dsmoke --projects :smoke-test
• Full project build clean (./compile.pl -DskipTests install)
• Assembly builds clean (./assemble.pl -Dopennms.home=/opt/opennms -DskipTests)
• No unused imports or dead code
• All test assertions use proper guards and error messages
• queryThanos() checks HTTP response code and includes error body
• resolveKarFile() deduplicated into CortexTestUtils with consistent error handling
• README Mermaid diagram and container table use correct ports
• Smoke tests pass on CI (Linux/Docker) — cannot run locally on macOS/podman due to pre-existing opennms/deploy-base amd64-only limitation

[cnewkirk]

Related PR: cnewkirk/opennms-cortex-tss-plugin#1 — Cortex TSS plugin changes including label values discovery optimization, multi-backend E2E smoke test harness (45 tests), and comprehensive architecture documentation.

The two PRs are complementary:

• This PR (OpenNMS repo): smoke test framework changes (INTEGRATION strategy, Thanos/Prometheus containers, CortexTssPluginIT)
• That PR (plugin repo): the plugin feature, standalone E2E harness, and documentation