restrictive version check limits usability of modified images

[maciejskorski]

With the current check of the image version format

https://github.com/overleaf/toolkit/blob/0ae6584650869d2aec9b703a9a54d41b14c76dfb/lib/shared-functions.sh#L13

it is impossible to run images with custom tags (e.g. those committed with a user-chosen version).

Users would like flexibility on versioning , e.g. to 5.0.5-updated-tex