Add setting to ignore 'Append link' when no files are open

Related to #701

Implements the feature to ignore the Append link option in Templates when no file is open, allowing file creation to proceed regardless. This feature is controlled by a new setting added to the Template choices.

Adds a new boolean property ignoreAppendLinkWhenNoActiveFile to the ITemplateChoice interface to support the feature.
Modifies TemplateChoiceEngine.ts to check the new setting and the presence of an active file before attempting to append a link, logging a warning if no active file is found and the setting is not enabled.
Updates templateChoiceBuilder.ts to include UI elements for enabling or disabling the ignoreAppendLinkWhenNoActiveFile setting, ensuring it is only displayed when the Append link option is enabled.
Updates the documentation in TemplateChoice.md to include information about the new setting, explaining its purpose and how it affects the behavior of the Append link option.

For more details, open the Copilot Workspace session.

chhoumann / quickadd

Add setting to ignore 'Append link' when no files are open #702