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?
registerFunctionsIn(factory);
    registerFunctionJoinGet(factory);
    registerFunctionFilesystem(factory);
    registerFunctionEvalMLMethod(factory);
    registerFunctionBasename(factory);
    registerFunctionTransform(factory);
    registerFunctionGetMacro(factory);
    registerFunctionGetScalar(factory);
    registerFunctionGetSetting(factory);
    registerFunctionIsConstant(factory);
    registerFunctionIsDecimalOverflow(factory);
    registerFunctionCountDigits(factory);
    registerFunctionGlobalVariable(factory);
    registerFunctionHasThreadFuzzer(factory);
    registerFunctionInitializeAggregation(factory);
    registerFunctionErrorCodeToName(factory);
    registerFunctionTcpPort(factory);
    registerFunctionByteSize(factory);
    registerFunctionFile(factory);
    registerFunctionConnectionId(factory);
    registerFunctionPartitionId(factory);
    registerFunctionIsIPAddressContainedIn(factory);
    registerFunctionQueryID(factory);
    registerFunctionInitialQueryID(factory);
#if USE_ICU
    registerFunctionConvertCharset(factory);
#endif
}
}