WT-13410: Switch Boost archive URL

JFrog is no longer offering webspace to Boost. They used to do this, but
this is costing them a lot. Boost now offers their own in-house URL to
download archives.

See:
- boostorg/boost#843 (comment)
- boostorg/website#900

P.S. while this isn't breaking for the builds, as this is cached. This
can result in breaking builds later, if the Dockerfile were to change.

jenkins/windows/Dockerfile

@@ -57,7 +57,7 @@ RUN choco install `
       7zip.install `
       -y
 
-ARG BOOST_URL=https://boostorg.jfrog.io/artifactory/main/release/1.81.0/source/boost_1_81_0.7z
+ARG BOOST_URL=https://archives.boost.io/release/1.81.0/source/boost_1_81_0.7z
 RUN powershell `
       -NoProfile `
       -ExecutionPolicy Bypass `