Improve client credentials entropy

[msokolovski]

Currently the code for generation of client id and client secret (RandomGenerator#96) has a weak entropy, which leaves gap for collisions and authentication errors.

The entropy can be improved with the following changes:

• switch all input generation components (random, time, thread ID) to Strings, in order to avoid numeric addition and produce more distinctive input string
• switch time component from milliseconds to nanoseconds, in order to achieve more frequent changes of the specific input
• add free memory as component for input generation

[rossitsaborissova]

Thanks for that improvement!