`pgconfigctl tune` doesn't work with the `Mixed` and `Desktop` profile types

[rodinasophie]

Dear pgconfig developers,

Thank you for the helpful tool for postgres parameters recommendations.

We have encountered the problem with the pgconfigctl tune.

According to the current implementation, when the profile is constructed via the Set() method, it always translates the profile string value to the uppercase, but the real value in the Profile enumeration starts with the capital letter, so the values never match.

Steps to reproduce:
pgconfigctl tune --profile=Mixed

Actual result:
invalid argument "Mixed" for "--profile" flag: must be one of [WEB OLTP DW Mixed Desktop]

Expected result:
The tuning works fine