[sessions] define a base instrumentor class

[axiomofjoy]

• should have an explicit span creation hook
• we need to support multiple priority levels depending on the importance of the semantic convention to make it less likely that important attributes are dropped

[axiomofjoy]

We need to identify as a team priorities for our existing semantic conventions.

[mikeldking]

Maybe we do a POC and evaluate the downstream impact. Could have issues with coupling our instrumentation to specifics of tracers and context managers that might have side effects.