In 8.0, the meaning of the parameter tcmallocReleaseRate changed and has different semantics from the 7.0 version.

In 7.0, the value had a server default of 1 and represented an internally defined rate of memory release. In 8.0, the default value is 0 and represents the number of bytes tcmalloc will release on top of the background thread.

We should add a start up warning so that any users that had explicitly set this value in 7.0 will be aware of this change after upgrading.