Add redirect for /solutions/gitlab-duo-pro/self-managed-and-gitlab-dedicated-trial/ to new target

Why is this change being made?

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Please add the details saying why, not just what in this section. Example: We have discussed the topic in Slack - (copy of Slack conversation). The current process is not efficient, this MR makes the description of X more clear, and helps move Y forward.

The trial workflow was changed on 2024-07-03, and therefore, https://about.gitlab.com/solutions/gitlab-duo-pro/self-managed-and-gitlab-dedicated-trial/ looks different. Old resources targeting the URL should be redirected to https://about.gitlab.com/solutions/gitlab-duo-pro/sales/

See Slack discussion: https://gitlab.slack.com/archives/C051SLP8WNB/p1720093871537819

Author and Reviewer Checklist

Please verify the check list and ensure to tick them off before the MR is merged.

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added, and the content is SAFE
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
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  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
  • The when to get approval handbook section explains the workflow in more detail
• For transparency, share this MR with the audience that will be impacted.
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Commits

• Add redirect for /solutions/gitlab-duo-pro/self-managed-and-gitlab-dedicated-trial/ to new target

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