Bump The Lounge to 4.5.2-rc.1

[MaxLeiter]

Summary

• bump Dockerfile THELOUNGE_VERSION to 4.5.2-rc.1
• add the 4.5.2-rc.1 changelog entry
• make scripts/update-version.sh portable on macOS/default sed and tolerant of the removed Makefile

Validation

• npm view thelounge@4.5.2-rc.1
• gh release view v4.5.2-rc.1 --repo thelounge/thelounge
• bash -n scripts/update-version.sh
• git diff --check
• ./scripts/update-version.sh 4.5.2-rc.1
• docker build --platform linux/arm64/v8 --load -t thelounge-docker:4.5.2-rc.1-test -f Dockerfile .
• docker run smoke test: thelounge --version, HTML title, no [ERROR] logs, config.js creation
• docker buildx build --platform linux/amd64,linux/arm64/v8,linux/arm/v7 --file Dockerfile .