Group web search related settings under a single webSearchSettings object for better organization.

Additionally, it introduces a new setting urlFetchBackend to control whether Jina or a local parser is used for fetching URL content.

merge changes from `file-search-fix` branch

…tions

This commit refactors the `parseInfioSettings` function to fix issues in error handling during settings migration, addressing issues that caused test failures. The changes also prevent excessive error logging in the terminal.

This commit introduces support for various web search backends, providing users with more options within the plugin.

Key Changes:
- Added multiple new search backends
- Modified the settings tab to include dropdown menus for selecting the preferred web search backends, along with corresponding API key input fields where necessary.

Current Supported Search Backends:
- SerpAPI
- Scrapingdog
- Serper
- Jina
- DuckDuckGo,
- Brave

This commit introduces a major refactoring of the settings schema to improve organization, maintainability, and future extensibility.

Key changes:
- Renamed `filesSearchSettings` to `fileSearchSettings`
- `migrateSettings` function is now moved to `migration.ts`. It can correctly handle schema migrations from older versions to the current one.
- Older, unused setting fields are now explicitly marked as deprecated within the settings schema to maintain backward compatibility while facilitating cleaner code.
- `DEFAULT_SETTINGS` has been updated to reflect the new structure, with some common schemas moved or reorganized.
- Tests for settings parsing have been updated to validate the new schema and migration logic.

Key Changes:
- Moved `SETTINGS_SCHEMA_VERSION` and `DeprecatedSettingsSchema` to `shared.ts`. This resolves a circular dependency, ensuring `SETTINGS_SCHEMA_VERSION` is correctly defined when migration objects are initialized.
- Simplified conditional checks within individual migration functions.
- Modified `parseInfioSettings` to first attempt strict parsing of current settings, deferring to the migration process only when an older or non-standard format is detected.

…ck-duck-scrape`

This commit temporarily hide the DuckDuckGo search option from the settings. This is due to unresolved issues with `duck-duck-scrape`.