refactor(dev-infra): do not validate config file multiple times (#38808)
refactor(dev-infra): do not validate config file multiple times (#38808)

Currently we validate the configuration file on each `getConfig`
invocation. We can only validate once since the configuration
is cached.

Also while being at it, renames the cache variables to lower-case as those
do not represent constants (which are convention-wise upper case).

PR Close #38808

angular/dev-infra,angular/dev-infra,angular/dev-infra,angular/dev-infra