Add link to Template Controller inside ecosystem page

[codablock]

This adds a link to the Template Controller on the ecosystem page, which I believe can extend Flux nicely with the same features that the ApplicationSet from Argo provides to Argo users. A blog post and announcement can be found here: https://medium.com/kluctl/introducing-the-template-controller-and-building-gitops-preview-environments-2cce4041406a. I was not sure if linking to that post would be appropriate as it does not explicitly use Flux resources in the examples.