21383: Update Salt installer formulas
I'm not aware of any specific reason we need this, but it's good
maintenance since I'm in here anyway.
letsencrypt 3.0.0 does introduce a backwards incompatible change because
it no longer installs the Apache plugin by default. Since we never
wanted that plugin and always specify the pkgs we want anyway, this
shouldn't affect us.
https://github.com/saltstack-formulas/letsencrypt-formula/blob/master/CHANGELOG.md#300-2021-07-02
Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>