Returns the resolved default cache size in MB as given by a Java system property, an
environment variable, or the
#DEFAULT_CACHE_SIZE_PERCENT, in that order of precedence.
The default maximum size can be given at startup by either the
GEOGIG_CACHE_MAX_SIZEargument either as a
#getMaximumSizeSystemProperty() or an
#getMaximumSizeEnvVariable().
If both are given, the system property takes precedence over the environment variable.
If none is given, the default maximum cache size defaults to a
#DEFAULT_CACHE_SIZE_PERCENT.