Filter non stork configs and read them as optional values

[aureamunoz]

Fixes #1201

[cescoffier]

Just 2 minor comments.

[cescoffier]

The Spring Boot config provider doesn't have the equivalent filtering / optional value handling:

for (String propertyName : getPropertyNames(environment)) {
    StorkConfigUtils.computeServiceProperty(propertiesByServiceName, propertyName,
            environment.getProperty(propertyName));
}

Should we add it there too?

[aureamunoz]

The Spring Boot config provider doesn't have the equivalent filtering / optional value handling:

for (String propertyName : getPropertyNames(environment)) {
    StorkConfigUtils.computeServiceProperty(propertiesByServiceName, propertyName,
            environment.getProperty(propertyName));
}

Should we add it there too?

Yes, I think so for consistency. I saw it at some point but didn't do. It's done in last commit.

[cescoffier]

See a few minor comments, but nothing is holding the merge.

[aureamunoz]

I need your approval again to merge