[Filestore] Allow configuring string truncation length before <truncated> in log

[Sazonov99]

In the current implementation, strings containing long values are automatically truncated when they reach the maximum length defined within the Google Protobuf library (see truncate_string_field_longer_than_).

This limit is hardcoded and cannot be changed through configuration. As a result, debugging information may be lost. For example:

DestroyFileStore #11304330866424255903 send response:  
Error { Code: 2147483650 Message: "Filestore volume \"***" h...<truncated>..."