Slightly reword action descriptions for better translations

Currently only one of the action descriptions in the Teslemetry integration uses the descriptive form of third person plural.

This commit changes the remaining descriptions to adopt the same language and changes "the" to "a" as the actual action target is defined below that in the UI.

homeassistant/components/teslemetry/strings.json

@@ -610,7 +610,7 @@
   },
   "services": {
     "navigation_gps_request": {
-      "description": "Set vehicle navigation to the provided latitude/longitude coordinates.",
+      "description": "Sets vehicle navigation to the provided latitude/longitude coordinates.",
       "fields": {
         "device_id": {
           "description": "Vehicle to share to.",
@@ -646,7 +646,7 @@
       "name": "Set scheduled charging"
     },
     "set_scheduled_departure": {
-      "description": "Sets a time at which departure should be completed.",
+      "description": "Sets the departure time for a vehicle to schedule charging and preconditioning.",
       "fields": {
         "departure_time": {
           "description": "Time to be preconditioned by.",
@@ -684,7 +684,7 @@
       "name": "Set scheduled departure"
     },
     "speed_limit": {
-      "description": "Activate the speed limit of the vehicle.",
+      "description": "Activates the speed limit of a vehicle.",
       "fields": {
         "device_id": {
           "description": "Vehicle to limit.",
@@ -702,7 +702,7 @@
       "name": "Set speed limit"
     },
     "time_of_use": {
-      "description": "Update the time of use settings for the energy site.",
+      "description": "Updates the time of use settings for an energy site.",
       "fields": {
         "device_id": {
           "description": "Energy Site to configure.",
@@ -716,7 +716,7 @@
       "name": "Time of use settings"
     },
     "valet_mode": {
-      "description": "Activate the valet mode of the vehicle.",
+      "description": "Activates the valet mode of a vehicle.",
       "fields": {
         "device_id": {
           "description": "Vehicle to limit.",