Match imagemagick between all environments

[michal-szostak]

All instance's version of imagemagick differ from version on production:

• production ImageMagick-6.9.10.68-4.el7.x86_64
• beta / master / pr imagemagick | 8:6.9.10.23+dfsg-2.1+deb10u1

The scope of this issue is to prepare docker images which can be used by beta / master / etc which would have the same version of imagemagick as the one used on production.

Additionally svg converter must be matched with the production version (new image magick must be compiled with rsvg support). See more: readthedocs/readthedocs-docker-images#131

Expected solution:

beta / master / pr instances should use ImageMagick-6.9.10.68-4.el7 with rsvg enabled.

Reason for this issue

1. Beta environment should match production as closely as possible - especially with dependencies
2. Current beta image magick has some bugs which cause infinite waiting times when processing some images