doc: Updates to reflect Project Cassini dependency

These are the following changes:
* Reflect the baremetal feature for EWAOL is inherited from
Project Cassini (meta-cassini).
* Reflect Docker container engine and K3s container orchestration
framework are inherited from Cassini.
* Add features provided by `cassini.conf`
* Update security hardening details.
* Update EWAOL dependency layers to include meta-cassini details.
* Update high level overview of the EWAOL project.
* Add meta-cassini repository related variables.

Issue-Id: OSSEMBEDA-1815

Signed-off-by: Vikas Katariya <vikas.katariya@arm.com>
Change-Id: Iaba55a368bfd453bfdbca980b464f70d5951f65e