Introduce "preset" config

[wata727]

See also terraform-linters/tflint#1056

This PR introduces the concept of "preset" to the ruleset config. The preset is for naming a group of rules so that you can use the rules you need without having to configure each rule individually. The idea was inspired by ESLint's "extends": "eslint:recommended".
https://eslint.org/docs/latest/user-guide/configuring/configuration-files#extending-configuration-files

This enables all rules that were previously disabled by default, and makes all rules available if not set. If you want to enable only some rules as before, set "recommended" to preset.

plugin "terraform" {
  preset = "recommended"
}

For compatibility, default to adopt preset="recommended" if no plugin "terraform" is declared. In other words, the rules that are enabled by default aren't much different than they used to be. However, at this time, we will review the rules that correspond to "recommended", so there may be differences in behavior.

[wata727]

Unlike the current settings, the following are enabled by default:

• terraform_deprecated_index
• terraform_required_providers
• terraform_required_version
• terraform_typed_variables
• terraform_unused_declarations
• terraform_unused_required_providers

These are the rules that I consider to be recommended even for senior engineers by my standards.

However, there are issues with https://github.com/terraform-linters/tflint/issues/1328 and https://github.com/terraform-linters/tflint/blob/v0.39.3/docs/rules/terraform_unused_declarations.md#how-to-fix, and the checks aren't perfect, so I'm not sure if these should be the default.

@bendrucker What do you think? If you have any other thoughts on the default rules, please let me know.

[bendrucker]

Yeah I'd say terraform_unused_required_providers needs to have the issue of implicit provider passing into modules addressed before it comes on by default. The others seem like good defaults for a "recommended" config.

[wata727]

OK, we will not include terraform_unused_required_providers in the default for now.

[bendrucker]

Nice! I think the concept of ruleset presets works well.