feat(config): adds support for top level file includes

[DelphicOkami]

Adds support for top level include directives in ssh config (IE: those outside of any blocks), writes changes back to the file containing the host's definition. If the host is defined in multiple files the user is presented with a selector to choose the file to write back to, this choice is then persisted as a file element in metadata.json, when this key is present for a host we skip the selector.

When writing changes back to an include file this ensures that only minimal changes are written back to prevent config duplication.

When adding new hosts this does not change the current behavior of writing them to the default ssh config.

Current limitations wildcard configuration and config using the Match directive are not mapped to any hosts during config editing

[DelphicOkami]

I know this solves the same issue as #76 but I wanted more comprehensive support