Release Version v2.15.3

[julianbrost]

Release Workflow

• Update ICINGA2_VERSION: Release 2.15.3 #10805
• Update bundled Windows dependencies: Bump OpenSSL shipped for Windows to v3.0.20 #10793
• Harden global TLS defaults (consult https://ssl-config.mozilla.org)
• Update CHANGELOG.md: Release 2.15.3 #10805
• Update doc/16-upgrading-icinga-2.md if applicable: not needed
• Create and push a signed tag for the version
• Build and release DEB and RPM packages
• Build and release Windows packages
• Merge dependency updates in https://github.com/Icinga/docker-icinga2/pulls
• Create release on GitHub
• Update public docs
• Announce release
• Forward-port the CHANGELOG changes to master: Forward-port v2.15.3 changelog to master branch #10812

Update Bundled Windows Dependencies

Update packages.icinga.com

Add the latest Boost and OpenSSL versions to
https://packages.icinga.com/windows/dependencies/, e.g.:

• https://master.dl.sourceforge.net/project/boost/boost-binaries/1.82.0/boost_1_82_0-msvc-14.2-64.exe
• https://master.dl.sourceforge.net/project/boost/boost-binaries/1.82.0/boost_1_82_0-msvc-14.2-32.exe
• https://slproweb.com/download/Win64OpenSSL-3_0_9.exe
• https://slproweb.com/download/Win32OpenSSL-3_0_9.exe

Update Build Server, CI/CD and Documentation

• doc/win-dev.ps1 (also affects CI/CD)
• tools/win32/configure.ps1
• tools/win32/configure-dev.ps1

Re-provision Build Server

Even if there aren't any new releases of dependencies with versions
hardcoded in the repos and files listed above (Boost, OpenSSL).
There may be new build versions of other dependencies (VS, MSVC).
Our GitHub actions (tests) use the latest ones automatically,
but the GitLab runner (release packages) doesn't.

[Al2Klimov]

Merge dependency updates in https://github.com/Icinga/docker-icinga2/pulls

• Bump golang.org/x/crypto from 0.47.0 to 0.50.0 in /entrypoint docker-icinga2#155