This is the combination of two small changes.
1. Add support for a string knob type.
2. Change profiles to be written to the log directory instead of the working
directory.
We have three options of where to write files: the working directory, the data
directory, and the log directory.
The working directory may be set to a non-writable location, and likely
contains the fdb binaries. Allowing these files to be overwritten would likely
not be a wise idea.
The data directory hosts our sqlite b-trees. It would also be very unfortunate
if these were ever overwritten by an unfortunate profile name.
The log directory contains logs. Out of the three, these matter the least if
they disappear or become corrupted.
Thus, we write to the log directory.
Trace Events are sampled and cached with an expiration set. Every TraceEvent above SevDebug is checked against this cache to see if it exceeded a set threshold. If yes, then throttle the TraceEvent.
If a TraceEvent is throttled, a warning msg is logged.
