emit a warning msg if invalid CLI configuration file location

[jbardin]

Fix-up and rebase of #32793

This Pull Request is about noticing people when TF_CLI_CONFIG_FILE environment variable points to a non existing file.

In such case, a warning message will be printed out like below;

There are some problems with the CLI configuration:
╷
│ Warning: Unable to open CLI configuration file
│
│ The CLI configuration file at
│ "/private/var/folders/7b/q4m7dd2x4fl8ltp731djsw940000gn/T/tmp.5TVZNsJu/.terraform.rcr"
│ specified does not exist.
╵

Fixes #32646

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

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