📖 Clarify that creating-a-cluster.md steps are creating a ROSA HCP cluster

[mjlshen]

What type of PR is this?
/kind documentation

What this PR does / why we need it:
The more explicit product name is ROSA HCP, see issue for more details

Which issue(s) this PR fixes:
Fixes #5257

Checklist:

• squashed commits
• includes documentation
• includes emojis

Release note:

NONE

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign stevekuznetsov for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• docs/book/src/topics/rosa/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[mjlshen]

/assign mzazrivec serngawy

Just as an fyi!

[k8s-ci-robot]

@mjlshen: GitHub didn't allow me to assign the following users: mzazrivec.

Note that only kubernetes-sigs members with read permissions, repo collaborators and people who have commented on this issue/PR can be assigned. Additionally, issues/PRs can only have 10 assignees at the same time.
For more information please see the contributor guide

In response to this:

/assign mzazrivec serngawy

Just as an fyi!

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-sigs/prow repository.