Update example custom components for 7.x

[jacobtylerwalls]

brief description of changes

In 7.0, the pattern for registering custom components changed slightly. See:

https://github.com/archesproject/arches/blob/77dcfef2322967163551b27dd34e4dbbd316e2ef/releases/7.0.0.md?plain=1#L176-L206

This box must be checked

• [x] the PR branch was originally made from the base branch

This box should be checked

• [ ] after these changes the docs build locally without error

This box should only be checked you intend to follow through on it (we can do it on our end too)

• [ ] I will cherry-pick all commits in this PR into other branches that should have them after this PR is merged