Add option to specify Golang default version

[creydr]

Currently the Go version for the dockerfiles is parsed from the go.mod file. This can lead to issues, when different components for a specific SO version lack behind (e.g. eventing is on 1.23, while SO requires through some dependencies 1.25, would lead to build issues for eventing).

This PR addresses it and allows to specify the default Golang version through the config files. It has the following order:

1. component specific version setting per branch (by setting for a component & branch e.g. in config/eventing.yaml) --> allows to override in specific cases
2. SO version specific version setting (by setting by branch in config/serverless-operator.yaml) -> should be the default to align all component versions for a SO release
3. Version in go.mod from component --> fallback

[dsimansk]

I'd consider returning (*string, error) and then work with nil, nil return in the generator to avoid additional input variable goModGoVersion string.

[dsimansk]

EOD it isn't simplifying a whole lot, so no hard opinion either way.

[creydr]

👍 updated it

[dsimansk]

/approve
/lgtm

if comments need to be addressed
/hold

[creydr]

/unhold
as review is addressed

[dsimansk]

/approve
/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: creydr, dsimansk

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