Finish the "encoder" test site

[giac-mysten]

Create a site that takes a Sui object ID of a Walrus site as input and returns the corresponding link to the site. The example can be added to the repository at MystenLabs/example-walrus-sites.

[Tzal3x]

Hey @giac-mysten , what is this issues about? Should we close it?

[giac-mysten]

I wanted to create a site that, given the Sui object ID of a walrus site, returns the link to the site itself. Probably a very quick thing if anyone want to pick it up for https://github.com/MystenLabs/example-walrus-sites