Fix: Failing to create template

[rafaeljusto]

The secret provided via argument (-e flag) was losing its value before listing the tools. This caused failures to connect to the MCP server.

mcp-registry/cmd/create/main.go

Lines 177 to 181 in 17fdb6e

	secrets = append(secrets, servers.Secret{
	Name: secretName(name, parts[0]),
	Env: parts[0],
	Example: "<" + parts[0] + ">",
	})

The strategy now is to replace the secret value only when encoding the object to generate the template.

There was also a missing --load flag when executing docker buildx build to correctly load the image into the memory.

WARNING: No output specified with docker-container driver. Build result will only remain in the build cache. To push result image into registry use --push or to load image into docker use --load