KAFKACTL_CONFIG should accept files without yml extension

[ThomasCAI-mlv]

Describe the bug

When providing the path to the config file to the KAFKACTL_CONFIG, if the config file doesn't have the .yml extension, any command line would fail.

To Reproduce

1. Put the kafkactl config file anywhere other than $HOME/.kafkactl/config.yml : myCustomPath/config
2. Set the environment variable KAFKACTL_CONFIG to myCustomPath/config
3. Run any command line
4. See error

Expected behavior

kafkactl should try to parse as yml file anyway for files without extension

Environment (please complete the following information):

• Kafkactl distribution and version: 1.18.0
• Ns4Kafka version: N/A

Steps taken to try and solve the problem

Additional context

N/A

[loicgreffier]

Related to #237