Add support for spot instances

[MarcelMue]

Please make sure in case you are changing the spec all our customers are informed beforehand.

You can throw a message in #sig-customer with the changes and the Solution Engineers will take care of
sharing the changes with the customers.

[marians]

I would prefer plural spot_instances_enabled over singular spot_instance_enabled, since a node pool is normally about a group of instances.

[marians]

I think adding all the spot capacity vs. on-demand capacity settings in V5AddNodePoolRequestNodeSpec does not fit the purpose of the V5AddNodePoolRequestNodeSpec (which is about the specification of a worker node). Some of the attributes should be moved one level up into V5AddNodePoolRequest.

[marians]

Actually, I don't feel as strongly after some more thinking. However, the comment

# Specification of a node in a node pool to be created
V5AddNodePoolRequestNodeSpec:

should be adapted to reflect the actual purpose better.

[marians]

Related to https://github.com/giantswarm/giantswarm/issues/8347

[marians]

Consistency thing: property names should use camel case. E. g. instance_distribution should be instanceDistribution.

Wrong PR, sorry!

[marians]

FYI: With the latest commits I also added default attributes to inform users about what we set as a default value if the attribute is not specified when creating a node pool.