Update docs for cross-tenant Basic/Standard restore support

[jhlodin]

https://cockroachlabs.atlassian.net/browse/DOC-13049

• Remove limitations that cross-tenant restores are unsupported on Basic/Standard
• Add additional step for cluster selection in Restore UI

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[github-actions]

Files changed:

• src/current/_includes/cockroachcloud/backups/cloud-api-restore-endpoint.md:
• src/current/cockroachcloud/managed-backups-advanced.md
• src/current/cockroachcloud/managed-backups.md
• src/current/cockroachcloud/managed-backups-basic.md
• src/current/cockroachcloud/managed-backups-advanced.md
• src/current/cockroachcloud/managed-backups-basic.md
• src/current/cockroachcloud/managed-backups.md

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