docs: replace all occurrences of “above” with “previous” in install and update docs

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What does this MR do and why?

Replaced every occurrence of the word “above” with the clearer term “previous” in the following files:

• doc/install/aws/_index.md
• doc/install/docker/configuration.md
• doc/install/docker/installation.md
• doc/install/installation.md
• doc/install/relative_url.md
• doc/update/background_migrations.md
• doc/update/deprecations.md
• doc/update/upgrading_from_source.md
• doc/update/versions/gitlab_15_changes.md
• doc/update/versions/gitlab_17_changes.md

References

Related to issue: #330052 (closed)

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