Standard manner to read properties and env vars for Testcontainers settings

[mdelapenya]

Comment from @sneko #399 (comment):

I just realised that I can set SkipReaper: true in the testcontainers.ContainerRequest struct so Ryuk is disabled. But that's hardcoded in the code, there is no way to manage it through an environment variable.

I looked a bit more at the code and doing a PR for this is a bit annoying because which would prevail if both are set? Considering TESTCONTAINERS_RYUK_DISABLED for all containers whereas SkipReaper is per request. But since by default SkipReaper is not a pointer it's always considered as false. So to not make breaking change the only solution would be to say, whatever the SkipReaper specified, TESTCONTAINERS_RYUK_DISABLED will override.

In the meantime since my CI/CD had an environment variable CI=true, I set SkipReaper according to it.

Ideas

Standardize how the testcontainers.properties file, and the ENV VARS are initialised, defining and documenting the right order of precedence.

[mdelapenya]

SkipReaper has been deprecated, so I think this discussion is not valid anymore.

On the other hand, having a consistent manner for loading env vars and props would be convenient.