Introduce `islm_version` in ISLM governance table

[shah]

To ensure that we can future-proof ISLM state management queries:

1. add a ISLM_VERSION PostgreSQL variable to the islm-infrastructure.psl codebase
   2, add a islm_version (TEXT) column to the governance table which defaults to using ISLM_VERSION configuration setting.

The islm_version column does not do anything right now but future iterations of ISLM might make different decisions based on the version.