Add --filter option

[wata727]

See also #1636

This PR introduces the --filter option as an alternative to file arguments. This is the same as the file argument, except that it doesn't check for the existence of the file:

$ tflint main.tf
$ tflint --filter=main.tf

Introduction of this option deprecates all arguments. It can be replaced as follows:

$ tflint --chdir=dir                  # replacement of "tflint dir"
$ tflint --filter=main.tf             # replacement of "tflint main.tf"
$ tflint --chdir=dir --filter=main.tf # replacement of "tflint dir/main.tf"

Arguments are still available, but will be removed in a future version, so early migration to --chdir/--filter is recommended.

[bendrucker]

This should probably be paired with an --exclude flag. And maybe should support glob patterns. Filtering out *.tf.json or some local convention like *-generated.tf seems like something users would want. It's possible to do in a shell script with find and repeated flags but the general idea with these flags is to avoid writing those wrapper scripts.

[wata727]

Good suggestion. Agreed that glob patterns are needed.
The original goal was to deprecate arguments, so I didn't include it that far, but I'll investigate if this PR addresses it.
The --exclude flag would be worth considering implementing in another PR.

[bendrucker]

Accidentally clicked close 🤦🏻‍♂️

[bendrucker]

Yeah --exclude can definitely be separate, happy to tackle that if you don't get to it. The reason globs seem essential is that we're steering people away from shell, and before users might have been relying on glob expansion in their shell:

tflint *.tf

[wata727]

Makes sense. I'm working on something else right now, so I'm happy if you could tackle implementing --exclude.