Changelog since v1.6.0-alpha.2

Changes by Kind

Adds release targets for both cmctl as well as kubectl-cert_manager (#4523, @JoshVanL)
CLI: Adds cmctl completion command for generating shell completion scripts for bash, zsh, fish, and powershell (#4408, @JoshVanL)
CLI: Adds support for auto-completion on runtime objects (Namespaces, CertificateRequests, Certificates etc.) (#4409, @JoshVanL)
Enable configuring CLI command name and registering completion subcommand at build time. (#4522, @JoshVanL)