fix(migration): check if ldap2 already exists (#9674)

# Which Problems Are Solved

With v2.71.0 the `idp_templates6_ldap3` projection was created but never
filled, as it was a subtable. To fix this we altered the
`idp_templates6_ldap3` to `idp_templates6_ldap2` with v2.71.5.
This was unfortunately without a check that the `idp_templates_ldap2`was
already existing, which resulted in an error in the setup step.

# How the Problems Are Solved

Add check if `idp_templates6_ldap2` is already existing, before renaming
`idp_templates6_ldap3` -> `idp_templates6_ldap2`.

# Additional Changes

None

# Additional Context

Closes #9669

cmd/setup/52/alter.sql

@@ -0,0 +1,2 @@
+ALTER TABLE IF EXISTS projections.idp_templates6_ldap3 RENAME COLUMN rootCA TO root_ca;
+ALTER TABLE IF EXISTS projections.idp_templates6_ldap3 RENAME TO idp_templates6_ldap2;