HM-488: Utilise the telmodel library and methods in ska-tmc-subarraynode

1. What this MR does / why we need it:

• Utilise the telmode library in ska-tmc-subarraynode

2. Make sure that you've checked the boxes below before you submit MR:

• No conflict with master branch.
• Merge Request Title appropriate.
• Unit/Integration tests added and existing test cases are passing.
• Variable and Function names state the purpose.
• There is no commented out code, print/debug statements.
• Logs are added wherever necessary.
• Exception is handled wherever required.