fix: add seo env variable to buildspec

[ludtkemorgan]

This PR addresses #(insert-number-here)

• Addresses the issue in full
• Addresses only certain aspects of the issue

Description

After adding ALLOW_SEO_INDEXING to the dockerfile it was still not being read because the build script doesn't have it as an argument

How Can This Be Tested/Reviewed?

This can only be tested in AWS pipeline

Author Checklist:

• Added QA notes to the issue with applicable URLs
• Reviewed in a desktop view
• Reviewed in a mobile view
• Reviewed considering accessibility
• Added tests covering the changes
• Made corresponding changes to the documentation
• Ran yarn generate:client and/or created a migration when required

Review Process:

• Read and understand the issue
• Ensure the author has added QA notes
• Review the code itself from a style point of view
• Pull the changes down locally and test that the acceptance criteria is met
• Either (1) explicitly ask a clarifying question, (2) request changes, or (3) approve the PR, even if there are very small remaining changes, if you don't need to re-review after the updates

[mcgarrye]

lgtm