Fixed TabletManagmentParameters serialization of replacements

[dlmarion]

TabletManagementParameters was still using a List<Pair<Path,Path>> for volume replacements serialization. This was changed to a Map<Path,Path> in other places of the code because there was an issue with Gson serialization. I added a test for serialization and deserialization and was able to successfully use a Map when setting enableComplexMapKeySerialization() on the Gson object.

Fixes #4107