Noticed while making changes in the JSON Schema generation, but we're
currently returning a mutable reference to all of our options, which
means that it might be possible to (accidentally) change configuration
options that then affects all of the running Renovate process.
To handle this, we can make sure to `Object.freeze` the options, as well
as making sure our types clarify this is read-only.
This isn't something that should be user-facing, but makes sure that
we're keeping these immutable.
We also need to make sure any modifications now return a new config
option.
When we return a default value, we need to return a clone, so it's not
the frozen default value, as that then means it can't be modified (i.e.
in tests).
Co-authored-by: Michael Kriese <michael.kriese@visualon.de>
Sergei Zharinov