Allow patching of EducationClass properties.

As described in #5410: add support for updating educationClass properties.
This adds the `UpdateEducationClass` to the `EducationBackend` interface,
and implements it on the `ErrEducationBackend` and `LDAP` backends.

It also alters `PatchEducationClass` to call the `UpdateEducationClass` method.

Closes #5410
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