There are several points to consider.
First: you can only install the packages that you have built with bitbake. So when you a list of progs you are missing in the image, it might be easiser to include those in the image recipe. There was a recent discussion in the forum, search for: "How do I configure additional rootfs(additional Directory, more Package like as lighttpd)?".
Second: during development it might come handy to have a package server on the development host PC. This is merely a web server providing debian (.deb) packages which were built with bitbake. All packages will be put under tmp-glibc/deploy/deb by bitbake. So when you want to install lighttpd on the target without putting it into the image, you can execute bitbake lighttpd on the build host and later install it on the target using dpkg.
Third: for in-the-field upgrades etc. the process is essentlially the same as above, but the web server is exposed in the internet and you have to master update safety and security. It might be easier and more reliable to do full image updates (using swupdate or such) especially if the boards run unattended.
Creating a .deb package manager is detailed e.g. here: https://yahiafarghaly.github.io/myblog/yocto/deb_package_manager/create-a-debian-package-manager-with-yocto.html and there are more similar tutorials around. But I'm not aware of a STM specific tutorial.
Yocto is very flexible and modular and therefore inherently complex.
hth
KnarfB
