Add certified templates tag and remove popular tag

[hemarina]

Introduce a "certified" tag/label for templates to highlight officially vetted templates. Remove the existing "popular" tag, as certification provides a more reliable quality signal for users.

[haileyhuber8]

We can use popular in as an option of sorting, but making sure we are prioritizing the quality certified templates and that "popular" correlates to forks or stars or provision/deployment numbers -- an actual definition marker of popularity so it has meaning.

This will involve creating criterion for what qualifies as a certified template, a system for testing as the template is submitted, periodically testing the templates to maintain the certified status, and documenting the process for becoming a certified template. We can work off the ai-app-templates gallery criteria as a start. We should be checking that the template will azd up and has our defined best practices as outlined in the contribution guide (such as security).