Implement RANDOMKEY command

[kelvinmwinuka]

Implement the RANDOMKEY command, which returns a random key from echovault (no database selection set yet).
Reference: https://redis.io/docs/latest/commands/randomkey/

Client-Server Spec:

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

Command: randomkey
Module: constants.GenericModule
Categories: constants.KeyspaceCategory, constants.ReadCategory, constants.SlowCategory
Description: (RANDOMKEY) Returns a random key.
Sync: false

Embedded Spec:

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

NOTE: You may have to edit the HandlerFuncParams type to include a function that returns a random key.