Add alias for last? parameter on environments page

What does this MR do and why?

last?, while usuable as a key in javascript, does not conform to the rest of the language very well. is_last, on the other hand, is more expected.

How to set up and validate locally

1. Enable feature flag Feature.enable(:new_environments_table)
2. Navigate to a project with deployments and check the network tab.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

For #347480 (closed)