[SchemaChange] SchemaChangeJobV2's persist method has problem

[morningman]

Describe the bug

1. Field partitionIndexMap in SchemaChangeJobV2 is not persisted.
2. Pair in indexSchemaVersionAndHashMap does not support GSON.

To Reproduce

1. create table
2. do a schema change
3. restart FE
4. meta replay error

This bug is introduced by #3705