Locked library versions

[jimrthy]

This has several specific versions pinned in requirements.txt.

That's a very unfriendly thing for a library to do.

I'm using poetry, and it refuses to add fastapi-opentracing to my project because I'm not using 0.61.1.

If there are changes in newer versions of the dependencies that break this library, that's one thing. But there should at least be a range of values that can work.