View and select attachment import location

[kepano]

Consolidating #3, #67, #229 regarding the location of assets

Currently importers follow the user's attachment preferences for Default location for new attachments defined in Obsidian app settings. This setting has the following options:

• Vault folder
• In the folder specified below (with a progressive disclosure field)
• Same folder as current file
• In subfolder under current folder

The problem

1. It is not clear when using Importer where the attachments will go.
2. Users may not know this option is configurable at the app level, or may want a different path for assets that come from an import.
3. Currently attachments may get overwritten or fail if they use the same file name. If two different attachments have the same name they should be deduplicated per @lishid's comment, see getAvailablePathForAttachment function

Requirements

• [ ] Add option to select attachment location to the Importer modal
  • [ ] Default to the user's app setting
• [ ] Make sure this works across all importer formats
• [ ] Deduplicate attachments with the same name, and update any links to those attachments