Allow arbitrary environment names

[NSeydoux]

We shouldn't use environment names as meaningful flags to enable or disable tests, but rather use specific feature flags. Thereforce, the environment name becomes only an informative property, and doesn't need any predefined values.

[jeswr]

If we are removing this gate, could you make any check that relies on environment variables vase insensitive.

I find this is useful for helping me catch this like using a lower-case s for Podspaces in my configuration.

[NSeydoux]

I'm not sure this will be possible in at least one critical place: environment names are mostly useful in the CI matrices, where they are used to bind to environments, and that comparison is strict. If the environment names mismatch, then the environment configuration (i.e. the secrets) will not be loaded, the the test will necessarily fail.

If that's valuable, we can keep the current restrictions, rotate dev-next to dev-2-1, and also add an escape hatch, like "custom", to specify when running this in CI against a freshly build version of the server, as opposed to a stable released one.

[jeswr]

I would be in favour of a "custom" option.