Automatic image optimization

[alb]

Completed a TODO in the get-contributors.js file.
This pull request adds automatic optimization of the contributors.jpg image using reSmush.it. One can also fine tune the image optimization level using the quality variable. I chose 75 as the current value after some testing as at this level the image is reduced in size, however it still retains enough quality to not impact the final look of the contributors list.
Alternatively squoosh could also be used to optimize the image, however I was unsure whether it's allowed to add a new dependency to the project or not. If it is please let me know and I can change the PR to use Squoosh.

This PR also removes the GitHub API tokens in the file, as the API route to fetch the contributors list doesn't require authentication.

Before submitting the PR, please make sure you do the following

• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with npm test and lint the project with npm run lint

[dummdidumm]

Approving, but someone who did this manually before should have a look, too

[benmccann]

I wonder if it might be better to use something like vite-imagetools once we've migrated to SvelteKit

[alb]

@benmccann that is probably a good idea since it would make it a lot simpler and more streamlined

[benmccann]

We could also do it for all images then and without an external API call. Let's try that route then. I got the site mostly converted to SvelteKit last night #6468, so I'll go ahead and close this one. I'd love some help with getting vite-imagetools setup after I finish getting the site converted. Thanks again for taking a stab at this!