Introduce support for the beast web frontend for the Ceph
RADOS Gateway which brings improvements to speed and scalability.
Default behaviour is changed in that for Octopus and later
(aside from some unsupported architectures) beast is enabled by
default; for older releases civetweb is still used.
This may be overridden using the 'http-frontend' configuration
option which accepts either 'beast' or 'civetweb' as valid
values. 'beast' is only supported with Ceph Mimic or later.
Closes-Bug: 1865396
Change-Id: Ib73e58e21219eca611cd4293da69bf80040f5803
c634aba6fd