Write a file `uuid` in server's data directory that contains random UUID, generated at startup if file does not exist.

It will be used for several purposes:
- to anonymously identify server in Sentry (currently Sentry is unusable);
- (possible future usage) to identify server in ensemble.

@tavplubix comments?
#if !defined(ARCADIA_BUILD)
#    include <config_core.h>
#endif
namespace DB
{
class FunctionFactory;
void registerFunctionCurrentDatabase(FunctionFactory &);
void registerFunctionCurrentUser(FunctionFactory &);
void registerFunctionCurrentProfiles(FunctionFactory &);
void registerFunctionCurrentRoles(FunctionFactory &);
void registerFunctionHostName(FunctionFactory &);
void registerFunctionFQDN(FunctionFactory &);
void registerFunctionVisibleWidth(FunctionFactory &);
void registerFunctionToTypeName(FunctionFactory &);
void registerFunctionGetSizeOfEnumType(FunctionFactory &);
void registerFunctionBlockSerializedSize(FunctionFactory &);
void registerFunctionToColumnTypeName(FunctionFactory &);
void registerFunctionDumpColumnStructure(FunctionFactory &);
void registerFunctionDefaultValueOfArgumentType(FunctionFactory &);
void registerFunctionDefaultValueOfTypeName(FunctionFactory &);
void registerFunctionBlockSize(FunctionFactory &);