[Blog post] Add post for the new `aspire doctor` command and CLI improvements

Please update/rewrite the blog PR and have it ready to merge before 10AM PT on your scheduled post date. Ping @BethMassi when you are ready to go and she will make it live on the blog. If you cannot make the date or have another topic idea, please let her know asap. Thanks!

PR: https://github.com/microsoft/aspire-blog/pull/27
Post date: 4/21