[CT-3445] [dbt/artifacts] Move FreshnessExecutionResultArtifact to a dbt/artifacts directory

[MichelleArk]

Housekeeping

• I am a maintainer of dbt-core

Short description

We'd like to begin moving our ArtifactMixin subclasses upstream of other core modules in order to decouple core's internal functional concerns from external data interfaces. Let's start with FreshnessExecutionResultArtifact - which has very few core dependencies to begin with - to get a new dbt/artifacts directory setup. This will involve moving the ArtifactMixin classes and other utilities in dbt.contracts to dbt.artifacts as well.

Long term, dbt/artifacts should not have any dependencies on dbt.core. Some of this will actually be pretty straightforward once the adapters decoupling is in! For example, we've moved most of the dependencies in contracts/results.py here into dbt/common in the feature/decouple branch: #8906

Acceptance criteria

FreshnessExecutionResultArtifact (and its necessary dependencies) are moved to a new dbt/artifacts directory. dbt/artifacts should have no dependencies on dbt.core unless they are being migrated to dbt-common in #8906 (e.g. base exceptions, logging, utils). Until the decoupling feature branch is in, we can keep those dependencies explicitly coming from dbt.core to avoid duplicating efforts.

Biggest risk is the dependencies. If we have to move the data class schemas then we will have to touch a lot of files.

Impact to Other Teams

N/A - should be a refactor.

Will backports be required?

nope

Context

No response