Use fnv1a instead of SHA256 to create images signatures

[jpreynat]

Because we use a private key alongside the URLs to sign server side, using a simpler and non-cryptographic hashing function such as fnv1a that can't be reversed should be secure enough.
It should eventually yield to way faster rendering on pages that have many images because we potentially compute these hashes for each image, and it will also make the resize endpoint faster too, since we need to recompute the hash there.

[argos-ci]

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Build	Status	Details	Updated (UTC)
default (Inspect)	👍 Changes approved	4 changed	Jun 24, 2024, 11:24 AM

[SamyPesse]

We can't just ship this as it'll break all images at the moment. We need a compatibility layer

[jpreynat]

@SamyPesse Done in 2a7104e

[SamyPesse]

It looks good, but we should test urls on preview url to ensure previous urls still work

[jpreynat]

Testing old images URLs using the previous algorithm from another deployment:

https://676a716a.gitbook-open.pages.dev/~gitbook/image?url=https%3A%2F%2F1050631731-files.gitbook.io%2F%7E%2Ffiles%2Fv0%2Fb%2Fgitbook-x-prod.appspot.com%2Fo%2Fspaces%252FNkEGS7hzeqa35sMXQZ4X%252Fuploads%252FYHeUUs1j7fxDUv8xxWVW%252Fcontent-editor.png%3Falt%3Dmedia%26token%3D992c96ed-1cf3-43da-b4c0-d7ca8bb2ed53&width=245&dpr=4&quality=100&sign=70577215f4d016f554c2232e4708a05a7fe32786e34f3094696c35d7b5c99071

Using a deployment from this branch with the old algorithm:

https://f7da6398.gitbook-open.pages.dev/~gitbook/image?url=https%3A%2F%2F1050631731-files.gitbook.io%2F%7E%2Ffiles%2Fv0%2Fb%2Fgitbook-x-prod.appspot.com%2Fo%2Fspaces%252FNkEGS7hzeqa35sMXQZ4X%252Fuploads%252FYHeUUs1j7fxDUv8xxWVW%252Fcontent-editor.png%3Falt%3Dmedia%26token%3D992c96ed-1cf3-43da-b4c0-d7ca8bb2ed53&width=245&dpr=4&quality=100&sign=70577215f4d016f554c2232e4708a05a7fe32786e34f3094696c35d7b5c99071

New URL from this branch (new algorithm):

https://f7da6398.gitbook-open.pages.dev/~gitbook/image?url=https%3A%2F%2F1050631731-files.gitbook.io%2F%7E%2Ffiles%2Fv0%2Fb%2Fgitbook-x-prod.appspot.com%2Fo%2Fspaces%252FNkEGS7hzeqa35sMXQZ4X%252Fuploads%252FYHeUUs1j7fxDUv8xxWVW%252Fcontent-editor.png%3Falt%3Dmedia%26token%3D992c96ed-1cf3-43da-b4c0-d7ca8bb2ed53&width=245&dpr=4&quality=100&sign=54cd6950&sv=1