Support for pymemcache 2.x and 3.x

[gregbuehler]

The pymemcache integration is currently locked to version 1.x. Current version is ~=3.5.

opentelemetry-python-contrib/instrumentation/opentelemetry-instrumentation-pymemcache/src/opentelemetry/instrumentation/pymemcache/package.py

Line 16 in 0b9e96d

_instruments = ("pymemcache ~= 1.3",)

[srikanthccv]

duplicate of #842