paragraphs_library_update_8103 does not check if paragraphs_library is in the enforced modules before being added

Problem/Motivation

If paragraphs_library_update_8103 is run multiple times, the config key `dependencies.enforced.modules` contains multiple copies of `- paragraphs_library` under the enforced modules. These update functions normally don't run multiple times on a single site, but I have a multisite case where it did.

Steps to reproduce

1. Run update on a site that needed the update.
2. Import configuration on another site that needs to run the update.
3. Run the update again

Proposed resolution

Add a check before adding module list to dependencies.
Perhaps add another update function to remove duplicate entries on sites?

Remaining tasks

User interface changes

API changes

Data model changes