Docs: Fix Vale issues with the Dependency Proxy topic

Problem to solve

The Vale linter is used to support grammar linting in GitLab documentation. As Vale was implemented after many of the GitLab documents were written, we have many documentation pages that do not meet the linting standards created by the GitLab Technical Writing team for Vale.

Further details

As an example, here's the output from a Vale test on the Dependency Proxy topic, which is in the docs here.

You don't need to fix all of these issues; fix as many as you can.

The first number is the line number in the doc file where you can find the issue.

 66:8   warning     Avoid using future tense:       gitlab.FutureTense    
                    "will then"                                           
 66:60  warning     Avoid using future tense:       gitlab.FutureTense    
                    "will cache"                                                           
 67:65  warning     Avoid using future tense:       gitlab.FutureTense    
                    "will get"                                            
 68:49  warning     Avoid using future tense:       gitlab.FutureTense    
                    "will serve"                                        

Proposal

Who can address the issue

Other links/references