v0.23.0 pre-release: Allow control of letter case of outputs

Known issues

• Does not interoperate with earlier versions of null-label. The canonical context = module.this.context fails if module.this.context is an older version
• context.tf does not incorporate var.label_key_case and var.label_value_case into the module.this object, preventing those variables from taking effect in the root module's module.this.

feat: add support for setting letter case of context tags @SweetOps (#107)

With this release, you gain control over the letter case of generated tag names and supplied labels, which means you also have control over the letter case of the ultimate id.

Labels are the elements you can include in label_order, namely namespace, environment, stage, name, and attributes. For every non-empty label, a corresponding tag name is generated. For namespace, environment, stage, the output is the formatted, normalized input. (By "normalized" we mean that it goes through regex_replace_chars.), For attributes, which is a list, each element is normalized, duplicates are removed, and the resulting list is converted to a string by joining the elements with the delimiter (defaults to hyphen). For name, which is special, the output is the same as id, which is the joining of the labels in the order specified by label_order and separated by delimiter.

• You can set label_key_case to one of upper, lower, or title, which will result in generated tag names in the corresponding case: NAME, name, or Name. For backwards compatibility, title is the default
• You can set label_value_case to one of upper, lower, title, or none, which will result in output label values in the corresponding case (with none meaning no case conversion of any kind will be done, though the labels will still be subject to regex_replace_chars). The case converted labels will show up not just in the module output of the labels themselves, but also in the tag values and in the id string.

You can look at the test cases in examples/complete and the expected results in test/src/examples_complete_test.go to see examples of how this is supposed to work.

One interesting example is that you can create ids in Pascal case by setting label_value_case = "title" and delimiter = "".