Config.getFile can be inferred from Config.currentContext

[manusa]

Description

Part of #6516

The field Config.file is used internally for refreshing the Config (Config.refresh) and persisting updated token values (OpenIDConnectionUtils.persistOAuthToken).

In addition, the field is exposed via Config.getFile, which is used downstream to evaluate if the Config was inferred from a file.
In #6240 this feature should be improved to include an additional Config.getFiles to retrieve the kubeconfig files that were evaluated when inferring the Config.

After the improvements in #6250 and others, the field is no longer needed, since this information is persisted in the NamedContext instances available at Config.currentContext and Config.contexts.

The values available here should be used instead and the fields and constructor/builder parameters should be removed.