Improve Help for build.sh

Using Ubuntu 22.04 because Debian has old packages ...

With Debian the Quay.io security checker found several issues in the
image. With Ubuntu we have never versions of all packages and therefore
less (or no) issues.

Build ARM64 images

Fixed comment and variable name

Updated image labels and build script

Used version number and remove explicit dependency

First version of Debian based image

Proposed fix for netbox-docker #765 -- SKIP_GIT will skip other git operations

Group the build output in GitHub Action

Add project version to Docker tag

Improved check ...

Co-authored-by: Christian Mäder <[email protected]>

Check if remote branch exists before checkout

Alpine update to 3.14

Format shell scripts with shfmt

Fix shellcheck complaint

NetBox should always be referred to as NetBox ...

Fix all instances of "Netbox".

```Shell
git ls-files -z . | xargs --null -I '{}' find './{}' -type f -print0 | xargs --null sed --in-place --regexp-extended 's#Netbox#NetBox#g;'
```

Ref: https://netbox.readthedocs.io/en/stable/development/style-guide/#branding

Gunicorn is replaced with nginx-unit ...

We now serve Netbox with an nginx-unit instance instead of Gunicorn.
This allows us to get rid of the extra Nginx container because Unit is
also serving the static files. The static files are now collected at container
buildtime instead of every startup.

Upgrade Python image to 3.9-alpine ...

Upgrade the default base image to Python 3.9 and start testing on Python 3.10-rc

Fix warning in Github Actions ...

Our build script is using "set-env" which has been deprecated by Github.
See this bolg entry:
https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

Move default source image to Python 3.8

Fix shellcheck error

Update build.sh ...

Include suggestion from cimnine

Co-authored-by: Christian Mäder <[email protected]>

Fixes build when DOCKER_FROM is set but empty ...

The DOCKER_FROM is set to an empty value in the push tests.
This expands the check to catch this test case

Fixed "latest" tag ...

The variable for the latest tag didn't contain all the needed values.

Let "latest" tag follow the highest version ...

Latest tag is now added to the new version when it is release by Netbox.

Fix shellcheck items found by shellcheck 0.7.1

Add checks to verifiy if a new build is needed ...

This checks if the source materials (python image, Netbox commit,
netbox-docker commit) have changed since the last build. This check is done
by comparing the digest and commit ids from the previous image with the
given tag to the current values taken from the Git and Docker repositories.

The checks are only performed for builds by the automated builds on Github.

Add labels for all variants ...

When we don't set the --label argument on the commandline for all
build variants we lose them in the image.
This also prints out the labes on image push.

Fix failing GH Action

Building the Docker image with Github Actions