Allow filtering of the image URL prior to generating image tags and alternate text

[petenelson]

Description of the Change

In instances where an image has been offloaded to a CDN, running the image CLI command is failing. This command calls generate_image_alt_tags(), which calls get_largest_acceptable_image_url(), which requires an image to be physically present on the server. If the image is not present, the image URL is null and no tags or alternate text can be generated.

Alternate Designs

None

Benefits

This pull request adds a filter to allow overriding of the image URL which can allow the Computer Vision API to pull the image directly from a CDN.

Possible Drawbacks

None

Verification Process

No verification was performed.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

• Added classifai_generate_image_alt_tags_source_url filter to allow overriding of the image URL within generate_image_alt_tags()

[jeffpaul]

This may resolve #201, but testing will be needed to be certain.

[dinhtungdu]

LGTM 👍