Update Puma config

[JPrevost]

Updates from Rails default to Heroku recommended Puma config.

Also adds rack-timeout which is recommended by Heroku to ensure requests are actually stopped when they timeout.

https://devcenter.heroku.com/articles/deploying-rails-applications-with-the-puma-web-server

https://mitlibraries.atlassian.net/browse/USE-396

Developer

Accessibility

• ANDI or WAVE has been run in accordance to our guide.
• This PR contains no changes to the view layer.
• New issues flagged by ANDI or WAVE have been resolved.
• New issues flagged by ANDI or WAVE have been ticketed (link in the Pull Request details above).
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New ENV

• All new ENV is documented in README.
• All new ENV has been added to Heroku Pipeline, Staging and Prod.
• ENV has not changed.

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Code

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  added technical debt.

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  (not just this pull request message).
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[coveralls]

Pull Request Test Coverage Report for Build 21840439223

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.123%

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Totals
Change from base Build 21833291499:	0.0%
Covered Lines:	1307
Relevant Lines:	1332

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💛 - Coveralls