[202311] Migrate GNMI table

[ganglyu]

What I did

We will use GNMI container to replace TELEMETRY container in public repo.
GNMI is using GNMI table for configuration, so we need to migrate configuration in CONFIG_DB.
For L2 mode, there's no GNMI configuration in minigraph, and there's no TELEMETRY table in CONFIG_DB, so we will not generate GNMI table.

Backport #3053

How I did it

If there's no minigraph and golden config, copy GNMI configuration from TELEMETRY table.
If there're minigraph and golden config, copy GNMI configuration from minigraph or golden config.

How to verify it

Run db migrator unit test, test with minigraph and test without minigraph.

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)