Add station callletters to SDR POC?

[bmpotter]

Some FM radio stations broadcast their call letters. This is useful to help users connect a frequency with an actual station, and to associate a station that is broadcast on multiple frequencies (usually by repeaters). It can also be useful to identify internet radio "stations".

• Add callletters column to stations table in db, as an additional key. (No automated migration - sdr is an example)
• Modify the sdr service to get the call letters from FM stations that broadcast it
• Modify the sdr service to put the url of internet radio "stations" (used for mocking) in the call letters field
• Modify the sdr2msghub service to add the callLetters field to the json sent to the cloud
• Modify the ibm functions action to put the call letters in the callletters column of the stations table
• Modify the sdr UI to query this value and show it in the edge node page

Part of epic https://github.ibm.com/Edge-Fabric/project-summary/issues/35