Support config files with well-known file names

[viswajithiii]

Right now, the config file is passed using the --config flag to kube-linter lint. In practice, however, users may want to have different configs (with different custom checks and different lists of enabled checks) for different apps, which may be in different directories or different Helm charts. Similar to .eslintrc files, we could support config files with a well-known filename, say .kube-linterrc, and have kube-linter lint automatically read them and merge them into the existing config as it walks directories.

[bdsoha]

A great addition to this issue would be allowing the search to also be based on an env variable:

export KUBE_LINTER_CONFIG=/path/to/the/config
kube-linter lint .