DOC-4117 examples for DEL, EXPIRE, and TTL commands (#333)

* DOC-4117 added EXPIRE examples

* DOC-4117 added TTL example

* DOC-4117 dotnet format changes

* DOC-4117 try to fix expire tests failing for Stack v6.2.6

* DOC-4117 improved SkipIfRedis attribute

* DOC-4117 dotnet format changes

Author: andy-stark-redis