Add env_name definitions to ConfigItem's that were missing them

[liamnichols]

Motivation

We leverage the xcov action in our Fastfile and it's great (thanks for the hard work so far 💪).

One thing we are trying to do however is keep our main Fastfile as lean as possible to make it easy for people to parse what is going on.

The problem that we face however its that sometimes, we are required to pass the same arguments to an action in multiple places, but the duplication in the Fastfile becomes a bit noisy.

Instead, we have a pattern where we set sensible global defaults in a hidden lane via the environment variable. What we'd like is to take this:

run_tests(coverage: true)
xcov(
  xccov_file_direct_path: Actions.lane_context[SharedValues::SCAN_GENERATED_XCRESULT_PATH],
  include_targets: XCOV_TARGETS.join(','),
  scheme: UNIT_TESTS_SCHEME,
  slack_channel: '#notifications-global-ios',
  slack_message: '',
  slack_username: 'Coverage Reporter',
  json_report: true,
  output_directory: File.join(OUTPUT_DIR, 'coverage'),
)

And instead have this:

run_tests(coverage: true)
xcov

While most of this is possible today, there are a couple of config items that don't currently have a env_name defined.

Changes

In this PR, I go through all of the options and I add the env_name definition if it was missing. I follow a relatively simple naming pattern of XCOV_{KEY_TO_UPPER_CASE}.