Remove env files support in the image builder

[Sawthis]

Description

Remove env files support in the image builder.

Reasons

Better solution without using env files was found.

Acceptance Criteria

[ ] check if someone is using env files e.g third-party-images, if yes migrate it to the solution with computing tags and dockerfiles before calling image builder
[ ] remove support for env files in the code
[ ] remove documentation connected with env files

Attachments

Support for env files was introduced in #10413