third_party/opentelemetry-cpp has an import.sh script that clones from mongodb-forks/opentelemetry-cpp, removes unneeded parts of the tree, and then applies patches.

This is a mix between the current way of vendoring code in third_party/ and older ways.

To do things the newer way, let's do the following:

• Apply patches/ as commits to the upstream mongodb-forks/opentelemetry-cpp branch. This is a good opportunity to explain the patches in commit messages.
• Move the source tree to third_party/opentelemetry-cpp/dist, instead of it being directly in third_party/opentelemetry-cpp.
• (optional) Rather than checking out the whole tree into a temporary directory, deleting sections of it, and then copying it into third_party/opentelemetry-cpp, instead use `git sparse-checkout` in place as was done for ASIO.