skip the update check at initialization if DISABLE_AUTO_UPDATE is set to true

Co-authored-by: Capybara <git.capybara@gmail.com>
Co-authored-by: drootang <drootang@users.noreply.github.com>
Co-authored-by: Augusto Souza <augustorsouza@gmail.com>
Co-authored-by: PatrBal <44707588+PatrBal@users.noreply.github.com>

Fixes #5244

Fixes #8998

Closes #7157

oh-my-zsh Changes the HISTSIZE and SAVEHIST values to fixed sizes,
however if a bigger value is set in ~/.zshrc, it will override it,
potentially causing the user history to be deleted.

So, only set these values if no other is set and if it is lower than the
default ones.

Closes #8981

Fixes #8786

Fixes #8925
Related #4688