doc: rename s023 to seoul

What

Renames in all documentation protocol s023 to Seoul.

Why

It should have been snapshotted initially as Seoul.

Anyways.

How

Grep for s023, rename to seoul, check, adjust.

Manually testing the MR

Check that the doc artifact is built well.

Contemplate the left menu in the doc, you should see "Seoul" instead of s023 (as in the current version online at https://octez.tezos.com/docs/.

Navigate to the protocol page (Changes in protocol versions / Protocol Seoul), and to the protocol-specific pages (Protocol Reference Manuals / Seoul Protocol Reference), and check that links to other pages work well.

You may also cd docs/ and make xrefscheck to verify that the labels seem right.

Checklist

• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR