Link to old page name in upgrading docs.

[mikelittle]

The page https://docs.altis-dxp.com/guides/migrating/ was previously at https://docs.altis-dxp.com/guides/migrating-from-wordpress/
Most of the links have not been updated leading to an unstyled page on the site.

Links on the following pages need to be updated:

• other-docs/getting-started/differences-from-wp.md
• other-docs/guides/README.md
• other-docs/guides/upgrading/README.md
• other-docs/guides/upgrading/v2.md
• other-docs/guides/upgrading/v3.md
• other-docs/guides/upgrading/v4.md
• other-docs/guides/upgrading/v5.md
• other-docs/guides/upgrading/v6.md
• other-docs/guides/upgrading/v7.md
• other-docs/guides/upgrading/v8.md
• other-docs/guides/upgrading/v9.md
• other-docs/guides/upgrading/v10.md
• other-docs/guides/upgrading/v11.md
• other-docs/guides/upgrading/v12.md
• other-docs/guides/upgrading/v13.md
• other-docs/guides/upgrading/v14.md

Acceptance criteria

• The links above are updated to the new path.
• The old page is removed from the site

[mikelittle]

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