Enable canary switching during spec execution

What does this MR do?

Enable QA specs to switch between canary and non-canary targets in mixed environment testing

Necessary framework changes for future mixed environment tests. See as an example: !70022 (merged)

Related to #338970 (closed)

How to setup and validate (cannot be validated locally, must execute against staging)

Example below:

1. Setup GDK per instructions to enable running tests locally targeting a remote server
2. Setup any necessary ENV vars such as your personal login information, assuming you have access to your target environment
3. Ensure you have a working spec tagged with mixed_env
4. Execute existing mixed environment test against staging or production only as these two environments are the only ones paired with canary environments.

   WEBDRIVER_HEADLESS=false bundle exec bin/qa Test::Instance::All https://<staging.>gitlab.com -- --tag mixed_env path/to/spec

   Please exercise caution and don't use system account credentials to run tests against prod especially.
5. Observe local browser step through the spec

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.