[Features][test-lib] Add message arg to the check function

I would like to propose a change to the check function of the dev-container-features-test-lib script.

The function should take a message to display when the test fails, like other testing frameworks have.

The current function code is:
https://github.com/devcontainers/cli/blob/c246645f97fba402c3b1b95983e573e92bcec464/src/spec-node/featuresCLI/utils.ts#L75-L91

I propose to add a message on $2 or the last argument.
Any thoughts on this?

I would suggest something like this:
```bash
check() {
LABEL=$1
MESSAGE = $2 or ${!#}

#
# the rest of the function
#
}
```

The new function should work like the examples below, and be backwards compatible

```bash
old:
check "java version LTS installed as default" \
grep "LTS" <(java --version)

new:
check "java version LTS installed as default" \
grep "LTS" <(java --version) \
"REASON: The installed version is: $(java --version)"

or

check "java version LTS installed as default" \
"REASON: The installed version is: $(java --version)" \
grep "LTS" <(java --version)
```