[common] pullSecret name should be configurable

[TobyTheHutt]

Is your feature request related to a problem? Please describe.
No.

Describe the solution you'd like
In the current state, the pullSecret can be turned on or off as a boolean . The name consists of the library.name variable and the suffix -registry-pull-secret, as described in the default values.yaml.

It's desirable in some use cases that the name of the secret can be set as a string.

Describe alternatives you've considered
If it's in one's power, they might change the naming concept of the K8s objects according to the common Chart. Alternatively, you might swallow the pill and rename/workaround the automatically generated secret with whatever mechanisms suit you best.

Additional context
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[nschmid]

Hi @TobyTheHutt
I think that has already been added a while ago. See: https://github.com/bedag/helm-charts/blob/master/charts/common/values.yaml#L45