Use imagestream generator for editing imagestream yaml files

[zmiklank]

• [x] httpd-container https://github.com/sclorg/httpd-container/pull/205
• [x] nginx-container
• [x] s2i-php-container https://github.com/sclorg/s2i-php-container/pull/441
• [x] varnish-container https://github.com/sclorg/varnish-container/pull/140
• [x] mariadb-container https://github.com/sclorg/mariadb-container/pull/232
• [x] postgresql-container https://github.com/sclorg/postgresql-container/pull/549
• [ ] s2i-nodejs-container https://github.com/sclorg/s2i-nodejs-container/pull/427
• [ ] s2i-python-container
• [ ] mysql-container
• [ ] redis-container
• [ ] s2i-perl-container
• [ ] s2i-ruby-container
• [ ] s2i-base-container
• [ ] create github action to check, if streams are up to date