feat(core): add scw.MergeProfiles command

[QuentinBrosse]

Usage example:

// Get Scaleway config active profile
config, _ := scw.LoadConfig()
configProfile, _ := config.GetActiveProfile()

// Get Scaleway env active profile
envProfile := scw.LoadEnvProfile()

// Get flag values
flagProfile := &scw.Profile{
	DefaultOrganizationID: scw.StringPtr("f121706b-2091-429b-a93a-c41b8ef4a068"),
}

// Merge profiles
profile := scw.MergeProfiles(configProfile, envProfile, flagProfile)

// Make custom validation or other stuff here...

// Create a Scaleway client
client, _ = scw.NewClient(scw.WithProfile(profile))

[jerome-quere]

LGTM