Replace two methods with a single one that returns the cert. This moves more
of the logic into the single caller (auto-config).
tlsutil.Configurator is widely used. By keeping it smaller and focused only on storing and
returning TLS config, we make the code easier to follow.
These two methods were more related to auto-config than to tlsutil, so reducing the interface
moves the logic closer to the feature that requires it.
This commit reduces the interface to Load() a bit, in preparation for
unexporting NewBuilder and having everything call Load.
The three arguments are reduced to a single argument by moving the other
two into the options struct.
The three return values are reduced to two by moving the RuntimeConfig
and Warnings into a LoadResult struct.
Reduce Jitter to one function
Rename NewRetryWaiter
Fix a bug in calculateWait where maxWait was applied before jitter, which would make it
possible to wait longer than maxWait.
