connectors: refactor spawn_source_handler takes 11 parameters

Split out of the #3795 review at hubcio's suggestion.

`source::spawn_source_handler` is at 11 parameters and carries `#[allow(clippy::too_many_arguments)]`. The natural fix is passing `&SourceConfig` instead of the individual fields.

That is blocked on a prerequisite: `SourceConnectorPlugin` needs the resolved-path/version split first, since the call site currently threads resolved values that are not on `SourceConfig`. So this is follow-up sized rather than a quick tidy, which is why it is an issue rather than a change in #3795.

No behaviour change intended, purely a signature and ownership cleanup.

Start with source::spawn_source_handler and trace its call site through SourceConnectorPlugin. Read the prerequisite resolved-path/version split and how SourceConfig currently represents the remaining values. Done means the handler accepts &SourceConfig, the resolved values are handled separately, and the too-many-arguments allowance can be removed without behavior changes.

Written by the indexing model from the issue text.