[flags/provider] handle alphabetically and in one place

[jonasbadstuebner]

Description
As in #3171 civo was forgotten to add to the flags description and was only added to the enum, I added civo to the list.
Also, to prevent this from happening in the future, I sorted the providers alphabetically.

And just to prove, that this is necessary, since I did an oopsie, there is a second commit, which readds providers that went missing when ordering.

Due to that and since there are a lot of providers, I put them into a seperate list, so we only have to maintain a single source of truth about the providers. The overview is bad otherwise.

Please DOUBLE CHECK, that all of them are in the list now!

Checklist

• Unit tests updated
• End user documentation updated

[jonasbadstuebner]

/assign @seanmalloy

[szuecs]

I validated that the list is correct via 3 files and loop with grep -q.

% for i in $(cat enum); do grep -q $i new 2>/dev/null || echo "$i not found"
done
[sszuecs@sandor-lab:/tmp/foo]% for i in $(cat enum); do grep -q $i providers 2>/dev/null || echo "$i not found"
done
zsh: exit 1     grep --exclude-dir=.svn --color -q $i providers 2> /dev/null
alibabacloud not found
zsh: exit 1     grep --exclude-dir=.svn --color -q $i providers 2> /dev/null
civo not found
zsh: exit 1     grep --exclude-dir=.svn --color -q $i providers 2> /dev/null
pihole not found
zsh: exit 1     grep --exclude-dir=.svn --color -q $i providers 2> /dev/null
plural not found

[szuecs]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: DrBu7cher, szuecs

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