global: change base to 8 for python 3.7 and 3.8, add locales

[ppanero]

replaces https://github.com/inveniosoftware/docker-invenio/pull/41

• Python 3.6: existing locales, due to glibc-common and they are set in line 46

  [root@6615771020cb src]# yum list installed | grep glibc
  glibc.x86_64                         2.17-324.el7_9              @updates
  glibc-common.x86_64                  2.17-324.el7_9              @updates
  glibc-devel.x86_64                   2.17-324.el7_9              @updates
  glibc-headers.x86_64                 2.17-324.el7_9              @updates
  [root@6615771020cb src]# echo $LC_ALL
  en_US.UTF-8
  [root@6615771020cb src]# echo $LANGUAGE
  en_US:en
  [root@6615771020cb src]# echo $LANG
  en_US.UTF-8

• Python 3.7 were being set explicitly at first

• Python 3.8 added in this PR