Feat: add import image features to move all images to OpenPlanner storage

[HugoGresse]

Close #87

The issue was that some images when not being reachable from ShortVid server, or some image links where going blank/being obsolete after some time (like the linkedin avatar)

This PR add a message on top of Sessions to let the user move the image to Openplanner storage (if possible)

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit cf52d30):

• https://conferencecenterr--pr135-feat-import-speaker-gc2z78hx.web.app
• https://apiopenplanner--pr135-feat-import-speaker-vqevan6f.web.app

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