templates: Add ability to ignore file depending on var

Because you've implemented templates by go template, we can use variables not only simple substitution but all abilities from go templates. For example if statements:

{{ if eq .expirationd "y" -}}
expirationd.init_module()

{{ end -}}

It's usefull to choose features from template. And that's great feature.

But we need to have the same ability with files themselves. To ignore them at all.

As suggest you can add only a few line here:

https://github.com/tarantool/tt/blob/550b7b04f996d10a3337a08ccef3f64ca9e870c6/cli/create/internal/steps/render_template.go#L35-L44

Somethink like that:
If file name after rendering is empty ".tt.template", we just ignore it

                 // Render file name.
                newFileName, err := templateCtx.Engine.RenderText(filePath, templateCtx.Vars)
                if err != nil {
                        return fmt.Errorf("failed file name processing %s: %s", filePath, err)
                }
+                if newFileName == ".tt.template" {
+                        continue;                        
+                }
                if newFileName != filePath {
                        if err = os.Rename(filePath, newFileName); err != nil {
                                return fmt.Errorf("error renaming %s to %s: %s", filePath, newFileName, err)
                        }
                }

Especially need to ignore directories

Start in cli/create/internal/steps/render_template.go at the file-name rendering and rename logic linked in the issue. Trace how rendered paths are handled for files and directories, then verify that paths rendering to .tt.template are ignored, including the requested directory case. Done means conditional template output can omit those paths without affecting other rendered files.