Replace GUARDED_BY with ABSL_GUARDED_BY in preparation for abseil upgrade#2283

ddelnano merged 2 commits intopixie-io:mainpixie-io/pixie:mainfrom

ddelnano:ddelnano/prepare-for-abseil-upgradeddelnano/pixie:ddelnano/prepare-for-abseil-upgradeCopy head branch name to clipboard