bug: local extension image still Failed to pull

### Bug description

`Extension.install()` always pulls first. On 1.4 a local image still raises `Failed to pull`. Master has #3649.

### Steps to reproduce

1. Build the image on the vehicle (`docker images` shows `name:tag`)
2. Install as a custom extension

### Primary pain point(s)

Local / offline install fails even when the image is already there.

### Additional context

https://discuss.bluerobotics.com/t/issues-installing-blueos-extension-locally/23066

Backport #3649 to 1.4. Skip pull if `_image_is_available_locally()`.

### Prerequisites

- [x] I have checked to make sure that a similar request has not already been filed or fixed.

Start by locating Extension.install() and _image_is_available_locally(), then compare the existing fix in master referenced by #3649. Reproduce the custom extension install with a prebuilt name:tag image shown by docker images; done means the local image installs without attempting a pull or raising Failed to pull.

Written by the indexing model from the issue text.