Add webp to processable formats

[danielfdickinson]

What does this PR change? What problem does it solve?
It adds webp as cover image 'processable format' so that webp images can also be responsive.

Was the change discussed in an issue or in the Discussions before?
No.

PR Checklist

• This change adds/updates translations and I have used the template present here.
• I have enabled maintainer edits for this PR.
• This change adds a Social Icon which has a permissive license to use it.
• This change does not include any CDN resources/links.
• This change does not include any unrelated scripts such as bash and python scripts.
• This change updates the overridden internal templates from HUGO's repository.

[adityatelange]

"Note that you need the extended version of Hugo to encode to WebP."
~ https://gohugo.io/news/0.83.0-relnotes/

PaperMod which in this case is free from the Extended Version of Hugo, which is why it is not included

[danielfdickinson]

Ah, ok. Feel free to close then (or would it be okay to add it as a configurable item)?
Or use a {{ if .IsExtended }} ... around webp? (there is a mechanism like that now).

[danielfdickinson]

According to Hugo Functions hugo.IsExtended was added in v0.83.0. To save time, I will update the PR using it, and if you don't want the PR, you can close it.

[danielfdickinson]

Moved to draft as changes required that will require testing.

[danielfdickinson]

That was far easier than expected. Do note this does bump the minimum required Hugo version to 0.83.0 (not part of this PR).

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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