docs: Fix link to the envtest documentation in the v1.0.0 migration guide

[timflannagan]

Update the v1.0.0.md migration guide and ensure the link to the envtest
documentation is correctly formatted.

Description of the change:

Motivation for the change:

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• Add a new changelog fragment in changelog/fragments (see changelog/fragments/00-template.yaml)
• Add or update relevant sections of the docs website in website/content/en/docs

[timflannagan]

That looks like it can be ignored:

  *  External link https://v1-10-x.sdk.operatorframework.io/ failed: response code 0 means something's wrong.
             It's possible libcurl couldn't connect to the server or perhaps the request timed out.
             Sometimes, making too many requests at once also breaks things.
             Either way, the return message (if any) from the server is: Couldn't resolve host name

[estroz]

/lgtm

[estroz]

/cherry-pick v1.8.x

[estroz]

/cherry-pick v1.9.x

[estroz]

/cherry-pick v1.10.x

[openshift-cherrypick-robot]

@estroz: new pull request created: #5109

In response to this:

/cherry-pick v1.8.x

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[openshift-cherrypick-robot]

@estroz: new pull request created: #5110

In response to this:

/cherry-pick v1.9.x

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[openshift-cherrypick-robot]

@estroz: new pull request created: #5111

In response to this:

/cherry-pick v1.10.x

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.