Default gemfile generator to puma >= 6.0

[jch]

Puma 5.x is not compatible with Rack 3 cookies. The current default new Gemfile uses puma ">= 5.0". Puma ~> 5.6 will error on start when used with Rack 3, but earlier versions will not.

puma/puma#3164: Support Rack 3 cookies
puma/puma#3166: Prevent loading with rack 3
phusion/passenger#2503: Related passenger issue detailing cookie error

Motivation / Background

This Pull Request has been created because new Rails apps can install versions of Puma which will silently set cookies incorrectly if used with rack 3.x

Detail

This Pull Request changes the base generator to default to puma >= 6.0

Additional information

Based on puma/puma#3164, would it make sense to backport this back to Rails 6.1?
/cc @JoeDupuis as original author on the puma side

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[zzak]

This is kind of similar to #49224, and I think it's true that edge Rails still supports Rack 2.

When running rails new, I get both rack 3.0.8 and puma 6.4.0, so I think there is no issue here.

Please correct me if I'm misunderstanding. 🙇

[jch]

Looks like my issue was fixed in main 10/16/22 545a990 when the puma version constraint changed from ~> 5.0 to >= 5.0. Rails 6.1.0 was released 12/9/2020, so the cookie issue exists for any projects created between 12/9/2020 rails 6.1.0 to 01/17/2023 rails 6.1.7.1

+1 this won't impact new projects going forward 🙏