Add support for UEFI HTTP boot

[elfosardo]

User Story

As an operator I would like to use the UEFI HTTP boot feature to be able to deploy bare metal hosts with boot over HTTP(s)

Detailed Description

HTTP boot is available since at least 9 years, it was standardized in UEFI version 2.5, and it's considered as a natural valid replacement for PXE boot.
It addresses PXE issues for security, relying on HTTPs and using a reliable TCP connection, and scalability and performance, for example with the possibility of using HTTP load balancers.
In general HTTP boot grants a faster, more reliable and more secure way to obtain operating system images and EFI executables during a network boot process.

Anything else you would like to add:

The ironic implementation is already done so we just need to add a new hardware driver to BMO to support it.

/kind feature

[elfosardo]

design proposal metal3-io/metal3-docs#459

[dtantsur]

/triage accepted