[MM-25647]: ability to permanently delete users (#14944)

Summary:
    Config option to allow permanent user deletion ServiceSettings.EnableAPIUserDeletion
    Expose permanent user deletion through API
    Local mode for delete user for use in mmctl

Ticket Link:
    Server part of https://mattermost.atlassian.net/browse/MM-25647

model/config.go

@@ -327,6 +327,7 @@ type ServiceSettings struct {
 	DEPRECATED_DO_NOT_USE_ImageProxyURL               *string `json:"ImageProxyURL" mapstructure:"ImageProxyURL"`         // This field is deprecated and must not be used.
 	DEPRECATED_DO_NOT_USE_ImageProxyOptions           *string `json:"ImageProxyOptions" mapstructure:"ImageProxyOptions"` // This field is deprecated and must not be used.
 	EnableAPITeamDeletion                             *bool
+	EnableAPIUserDeletion                             *bool
 	ExperimentalEnableHardenedMode                    *bool
 	DisableLegacyMFA                                  *bool `restricted:"true"`
 	ExperimentalStrictCSRFEnforcement                 *bool `restricted:"true"`
@@ -699,6 +700,10 @@ func (s *ServiceSettings) SetDefaults(isUpdate bool) {
 		s.EnableAPITeamDeletion = NewBool(false)
 	}
 
+	if s.EnableAPIUserDeletion == nil {
+		s.EnableAPIUserDeletion = NewBool(false)
+	}
+
 	if s.ExperimentalEnableHardenedMode == nil {
 		s.ExperimentalEnableHardenedMode = NewBool(false)
 	}