Ignore files and preview diffrences functions during update (developer mode ON only)

[therampagerado]

• Added a new PREVIEW_FILE action and logic for excluding user-selected files from updates, enabling merchants to skip specific files during the update process
• Expanded the client-side updater to send ignored file paths and fetch preview data from the server for on-demand comparison
• Enhanced the update results template with preview links, ignore checkboxes, and a modal showing current vs. new file contents before applying updates
• New function is only visible with module's developer mode ON. A new warning is displayed.

Usefull if merchant/developer has knowledge of which local files were changed (during testing, debugging) but wants to easily introduce new updates in other files.