Allo implicit acces to files mentioned in the prompt

### Describe the feature or problem you'd like to solve

Sometimes it is useful to refence an external file (e.g. documentation or other examples) and then copilot ask to access this file out of the allowed list. As its quite obvious I want it to access that file it would be good if implicit access could be granted (read only).

### Proposed solution

There should be some `--grant-implicit` flag that if I mention a file or website in my prompt grants read only access to that resource even if outside the current allowed directory range.

### Example prompts or workflows

Something like:

> The documentation at /home/myuser/balbal.txt describes how we need to implement the new feature X in this session, make you familiar with that and create a plan.

or

> Our implementation of A violates section abc of specification at http://example.test/rfc123.txt and we need to make it compliant.

### Additional context

_No response_