[YANG] Fix issue: Non compliant leaf list in config_db schema

[Junchao-Mellanox]

Why I did it

Fix issue: Non compliant leaf list in config_db schema

How I did it

The basic flow of DPB is like:

1. Transfer config db json value to YANG json value, name it “yangIn”
2. Validate “yangIn” by libyang
3. Generate a YANG json value to represent the target configuration, name it “yangTarget”
4. Do diff between “yangIn” and “yangTarget”
5. Apply the diff to CONFIG DB json and save it back to DB

The fix:
• For step #1, If value of a leaf-list field string type, transfer it to a list by splitting it with “,” the purpose here is to make step#2 happy. We also need to save <table_name>..<field_name> to a set named “leaf_list_with_string_value_set”.
• For step#5, loop “leaf_list_with_string_value_set” and change those fields back to a string.

How to verify it

1.Manual test
2. Changed sample config DB and unit test passed

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111

Description for the changelog

Link to config_db schema for YANG module changes

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