Add redirect for removed block editor tutorial.

[ndiego]

WordPress/gutenberg#53159 consolidates the Building a custom block editor and Tutorial: building a custom block editor into one doc. This PR adds a redirect from the removed tutorial doc to the main page.

Once #53159 is merged, this redirect will be needed.

[adamwoodnz]

LGTM

[dd32]

This PR is against the not-yet-released developer theme, it'll need to be applied to the old branch to apply to the currently deployed developer.wordpress.org.

(This change still needs to be made, it just needs an additional commit to the other branch)

Changes needed

[ndiego]

@dd32 this branch, right?

[ndiego]

Switching branches caused a bit of a mess on this PR, so I just created a fresh one here.

[ndiego]

@dd32 It doesn't appear that the redirect is working. Navigating to https://developer.wordpress.org/block-editor/how-to-guides/platform/custom-block-editor/tutorial/ leads to a 404 when not logged in. Did I mess something up?

[dd32]

@ndiego I think I failed to actually deploy this change, sorry about that! should be fixed now:

$ curl -Is 'https://developer.wordpress.org/block-editor/how-to-guides/platform/custom-block-editor/tutorial/' | grep -Ei '^(HTTP|Location)'
HTTP/2 301
location: https://developer.wordpress.org/block-editor/how-to-guides/platform/custom-block-editor

[StevenDufresne]

I ran the sync. Try it now.

[juanmaguitar]

The redirection works now. Thanks!