feat(assets): add the ability to disassociate an uploaded asset from a well

[TylerAdamMartinez]

Why

This PR addresses the following problem/context:

• Add an endpoint to update an Asset's Thing association without modifying the Asset itself.
• Allow assets to be reassigned to a different Thing or disassociated entirely.

How

Implementation summary - the following was changed/added/removed:

• Add a new PATCH /asset/{asset_id}/association endpoint.
• Add AssetAssociationUpdate and AssetAssociationResponse schemas.
• Add audit logging when creating new associations

Notes

Any special considerations, workarounds, or follow-up work to note?

• This endpoint only updates the Asset <-> Thing association; it does not modify Asset metadata.
• Existing associations are removed before creating a new one, ensuring an Asset is associated with at most one Thing.
• Passing thing_id: null removes all Thing associations while preserving the Asset record.

[likithabommasani21]

Looks good to me