[shelly] Correct LoRa airtime description wording

The Add-On's air_time_hr_ms is not cumulative; Shelly defines it as
transmission time during the last 60 minutes. Update the channel-type,
i18n and README descriptions to match, so the UI doesn't imply
lifetime/persisted semantics.

Signed-off-by: Markus Michels <markus7017@gmail.com>

Author: markus7017

bundles/org.openhab.binding.shelly/README.md

@@ -642,7 +642,7 @@ The add-on firmware version is shown in the Thing property `addonFirmware`; the
 |         | errorsTx     | Number            | yes       | Number of failed transmissions to the LoRa network.                               |
 |         | snr          | Number:Dimensionless | yes   | SNR (signal-to-noise ratio in dB) of the last received packet.                    |
 |         | rssi         | Number:Power      | yes       | RSSI (received signal strength in dBm) of the last received packet.               |
-|         | airtime      | Number:Time       | yes       | Cumulative transmission air time in milliseconds.                                 |
+|         | airtime      | Number:Time       | yes       | Transmission air time of the LoRa Add-On during the last 60 minutes.              |
 
 ### Shelly 1 (thing-type: shelly1)
 

bundles/org.openhab.binding.shelly/src/main/resources/OH-INF/i18n/shelly.properties

@@ -943,7 +943,7 @@ channel-type.shelly.loraTxBytes.description = Number of bytes sent to the LoRa n
 channel-type.shelly.loraTxErrors.label = TX Errors
 channel-type.shelly.loraTxErrors.description = Number of failed LoRa transmits
 channel-type.shelly.loraAirtime.label = Airtime
-channel-type.shelly.loraAirtime.description = Cumulative on-air time of the LoRa Add-On
+channel-type.shelly.loraAirtime.description = Transmission air time of the LoRa Add-On during the last 60 minutes
 channel-type.shelly.loraSignal.label = LoRa Signal Strength
 channel-type.shelly.loraSignal.description = Received Signal Strength (RSSI) of the last received LoRa packet
 channel-type.shelly.loraSNR.label = SNR

bundles/org.openhab.binding.shelly/src/main/resources/OH-INF/thing/shellyGen2_relay.xml

@@ -785,7 +785,7 @@
 	<channel-type id="loraAirtime" advanced="true">
 		<item-type>Number:Time</item-type>
 		<label>Airtime</label>
-		<description>Cumulative on-air time of the LoRa Add-On</description>
+		<description>Transmission air time of the LoRa Add-On during the last 60 minutes</description>
 		<category>Time</category>
 		<tags>
 			<tag>Measurement</tag>