Add preliminary in-tree CI infrastructure for developers

The goal of this project is to integrate the relevant scripts from the
FreeBSD-CI project (https://github.com/freebsd/freebsd-ci) into the sr

Add preliminary in-tree CI infrastructure for developers

The goal of this project is to integrate the relevant scripts from the
FreeBSD-CI project (https://github.com/freebsd/freebsd-ci) into the src
repository. This allows developers to run the test suite similar to how
it is executed on ci.freebsd.org, and eventually, have it directly used
by our CI system. This effort is also part of the workflow improvement
project, aiming to incorporate pre-merge testing.

Current Features:
* Does smoke tests using either bhyve(amd64 only) or qemu(Non x86_64 or
when defined USE_QEMU=1). Currently defined CITYPE=smoke. Once we have
added full tests we can also utilize something like CITYPE=full
* Most of the resources are dynamically allocated based on available
resources in the host
* If CPU supports POPCNT or vmm can be loaded then bhyve is used for
amd64 otherwise automatically installs and uses qemu@nox11
* When required third party applications or packages for booting non-x86
images are automatically installed

Current Limitation:
* Does not support full tests like the one in our Jenkins
* At this moment this is also not suitable to be used in our Jenkins
platform as the jobs are divided in multiple smaller tasks and
artifacts are moved here and there which are not exactly the scenario
for individual developers.

Future Works:
* Add full tests like the one in ci.freebsd.org
* Add different tests or options to disable some tests
* Add test profiles full
* Possibly add test through Cloud Providers like AWS/GCP/Azure or Cirrus
or Github Actions
* Update documentation

Test Plan:
cd /usr/src/tests/ci
make ci
make TARGET=amd64 TARGET_ARCH=amd64 ci
make TARGET=amd64 TARGET_ARCH=amd64 USE_QEMU=1 ci
make TARGET=arm64 TARGET_ARCH=aarch64 ci
make TARGET=powerpc TARGET_ARCH=powerpc64 ci
make TARGET=powerpc TARGET_ARCH=powerpc64le ci
make TARGET=riscv TARGET_ARCH=riscv64 ci

Reviewed by: lwhsu
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D43786

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