Implement GETDEL command

[kelvinmwinuka]

Implement the GETDEL command, which gets the current value at the specified key and then delete the key.
Reference: https://redis.io/docs/latest/commands/getdel/

Client-Server Spec:

Command File: ./internal/modules/generic/commands.go
Test File: ./internal/modules/generic/commands_test.go

Command: getdel
Module: constants.GenericModule
Categories: constants.WriteCategory, constants.FastCategory
Description: (GETDEL key) Get the value of key and delete the key. This command is similar to [GET](https://redis.io/docs/latest/commands/get/), except for the fact that it also deletes the key on success (if and only if the key's value type is a string).
Sync: true

Embedded Spec:

Command File: ./echovault/api_generic.go
Test File: ./echovault/api_generic_test.go