2.4.1rc1: Add more XGBoost features

What's Changed

• [2.4] tf dataset setup and teardown by @SYangster in #2365
• [2.4] Update outdated links by @YuanTingHsieh in #2367
• [2.4] Fix nemo example link by @holgerroth in #2374
• [2.4] Fix NEMO links by @YuanTingHsieh in #2384
• [2.4] Update license headers by @YuanTingHsieh in #2386
• [2.4] Add xgboost histogram_based_v2 by @YuanTingHsieh in #2382
• [2.4] Clean up file pipe by @YuanTingHsieh in #2391
• [2.4] Added ReliableMessage by @nvidianz in #2394
• [2.4] Add xgboost example, unit tests, integration tests by @YuanTingHsieh in #2392
• [2.4] Add xgboost metrics tracking cb by @YuanTingHsieh in #2381

Full Changelog: 2.4.0...2.4.1rc1