remove unnecessary word in docs: 'an'

Per Brant's comment in:
    https://review.openstack.org/#/c/99075/3/doc/source/http-api.rst

Change-Id: I7d4b6d46666a71601f30da48bd720f847a8dfa09
Corrects minor spelling mistakes

Change-Id: Ib603861ad19a525c112153ac3799f2cbe453d4f7
the user_tenant_membership table was replaced by "assignment"

This updates some help text to reference the new assignment table rather
than the old table.

Change-Id: I69d1ef4e788a58e3f15104ff9083cf5a4c8dc761
deprecate LDAP config options for 'tenants'

This deprecates all config options using the term 'tenant' in favor of
new options using the term 'project'.

Change-Id: I7eb6819de33f4d94a8bae75286bb02436152c64b
Closes-Bug: 1283841
Merge "remove unnecessary word in docs: 'an'"
Merge "deprecate LDAP config options for 'tenants'"
Merge "Corrects minor spelling mistakes"
Merge "the user_tenant_membership table was replaced by "assignment""