SGM-6984 - Update Tailwind custom spacing

[gitstart-app[bot]]

This PR was created by GitStart to address the requirements from this ticket: SGM-6984. This ticket was imported from: SGM-6984

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Description:

Updated the spacing scale to the new scale specified on the figma link: https://www.figma.com/design/o1QRtdQI0ozKq0n7ATrKlx/Marketing-DLS?node-id=7649-36393&m=dev

Note: 4xl spacing was subsitituted for name #16

• [Sourcegraph Issue] https://github.com/sourcegraph/about/issues/6984
• [Ticket] https://clients.gitstart.com/sourcegraph/3436/tickets/SGM-6984

DEMO:

https://www.loom.com/share/61a970b7e5304dd798d4c42f3cd693d9?sid=11e88915-9b6b-43e2-be9d-f12804ddd8e2

Test Cases:

• [x] Upated spacing name and values match those provided in the figma design

• [x] Old spacing scale name values are accounted for in the new design

• [x] Old spacing names are updated to the new naming across the site

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[traceyljohnson]

@gitstart-sourcegraph This is good to merge. Can you resolve the conflicts?