ConfigRecorder: fix value changed check with null build-time values

[SIMULATAN]

This is a fix for a bug I encountered in production where the whole application would crash with a cryptic message:

After remote debugging it, I found the problem to be the particular line I changed. The bug occurs when a build-time property is null as it tries to call equals on this value to check for runtime config changes.

One case in which this happens is when environment variables that aren't set are used in a config value. In particular, using, say, $POSTGRES_USER as a variable in %prod.quarkus.datasource.url causes the build-time value to evaluate to null with rawValue being the property without the variables substituted.

This PR changes the logic to use Objects.equals which is null safe. If the build-time value is null, it'll detect it as a change (as long as the runtime value isn't null too)

Note for maintainers: the commit is unsigned as I recently changed my email and haven't updated my PGP key. Squash merge the PR to sign the commit with GitHub's key

[quarkus-bot]

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