add st2-auth-backend-pam to legacy requirements files

Author: cognifloyd

requirements.txt

@@ -66,6 +66,7 @@ simplejson
 six==1.17.0
 sseclient-py==1.8.0
 st2-auth-backend-flat-file
+st2-auth-backend-pam@ git+https://github.com/StackStorm/st2-auth-backend-pam.git@master
 st2-auth-ldap@ git+https://github.com/StackStorm/st2-auth-ldap.git@master
 st2-rbac-backend@ git+https://github.com/StackStorm/st2-rbac-backend.git@master
 stevedore==5.3.0

st2auth/in-requirements.txt

@@ -9,4 +9,6 @@ stevedore
 # For backward compatibility reasons, flat file backend is installed by default
 st2-auth-backend-flat-file
 st2-auth-ldap@ git+https://github.com/StackStorm/st2-auth-ldap.git@master
+# This requirement has been injected by st2-packages.git for many years.
+st2-auth-backend-pam@ git+https://github.com/StackStorm/st2-auth-backend-pam.git@master
 gunicorn

st2auth/requirements.txt

@@ -13,5 +13,6 @@ passlib==1.7.4
 pymongo==4.6.3
 six==1.17.0
 st2-auth-backend-flat-file
+st2-auth-backend-pam@ git+https://github.com/StackStorm/st2-auth-backend-pam.git@master
 st2-auth-ldap@ git+https://github.com/StackStorm/st2-auth-ldap.git@master
 stevedore==5.3.0