feat: pointers for multi level configuration

**What would you like to be added**:

Syft's config options should be updated to use bool ptrs in order to allow for proper multi-level configuration. This allows for the distinction between `false` and `unset` values.

**Why is this needed**:
It's unclear if the default `false` zero value can behave correctly when trying to decide on values between config levels

**Additional context**:
See this comment from an earlier PR:
https://github.com/anchore/syft/pull/2274#discussion_r1380651432

Start by locating Syft's configuration option definitions and the code that combines values across configuration levels. Read the linked discussion in PR #2274 for the intended behavior. Done means boolean options distinguish false from unset and resolve correctly across multiple configuration levels, with tests covering those cases.

Written by the indexing model from the issue text.