We can now tune the value of TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES by
setting an annotation on the CephCluster CRD like so:
```
annotation:
osd:
TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES: "134217728"
```
Alternatively, if nothing is specified Rook will read the value of the
file `/etc/sysconfig/ceph`.
Closes: https://github.com/rook/rook/issues/6134
Signed-off-by: Sébastien Han <seb@redhat.com>