Add diff log to env:pull command

[khamilowicz]

Why

ENG-15251: Analyse EnvVar UI feedback from user

Users should be aware of the changes that the command env:pull performs: new, changed, and deleted variables should be clearly visible.

How

• Added diff

Test Plan

1. Execute eas env:pull --environment ENVIRONMENT - all variables should be displayed in normal text, without prefixes
2. Add, delete, and change some variables (via website or CLI)
3. Pull variables again

• New variables are displayed in green text with a + prefix.
• Deleted variables are displayed in red text with a - prefix.
• Changed variables are displayed in yellow text with a ~ prefix.
• Unchanged variables remain in black text without any prefix.

Verify for plain text, sensitive, secret, text and file variables.