LTS: Configure percent used value to check safe storage limit

[sachin-j-joshi]

Is your feature request related to a problem? Please describe.
Currently the storage safe limit (storage.safe.size.bytes.max)is an absolute value which is prone to be misconfigured. This results invalid configuration. It is also difficult to set default value.

Describe the solution you'd like
Instead, it is convenient for user to set percent used value (with default value of 90%).
New config value is added safe.size.used.percent.max
For backward compatibility continue to support absolute value for storage.safe.size.bytes.max. The lower of the threshold triggers safe mode.

Describe alternatives you've considered
Not using percent used leads to error prone configs.

Additional context
Add any other context or screenshots about the feature request here.