update cmake version and add ninja

[ciros88]

here two requests:

• the first is to update cmake since 3.20 seems old nowadays (lot of cmake scripts have an higher version requirement)
• the second it is a request for adding ninja package, since it is too common and widely used

little note: currently i do both of above mentioned things by myself extending your image, but seems i'm forced to execute:

RUN pacman-key --init && pacman -Sy archlinux-keyring --noconfirm && pacman -Syu --noconfirm ninja

i think u could embed this keyring stuff in your image in order to facilitate who extends it

thanks