Allow plugins to extend the categories of the Publisher Library

[NateWr]

Describe the feature
The Publisher Library allows journal managers to upload files to one of four categories. These categories are fixed and cannot be modified.

I propose that we add hooks which allow plugins to extend the categories. This will allow a plugin to make use of files uploaded to the Publisher Library.

Use Case
I have two clients who want a consistent way for journal managers to upload and manager logos for their partner institutions. This is a common challenge which journals often solve by injecting logos into the pageFooter, additionalHomepageContent, or a custom sidebar block.

These approaches do not provide sensible design constraints, so logos are often wildly different sizes and not aligned well. You can see some common examples of this UI pattern here and here.

What application are you using?
3.3.x

Additional information
If the PRs are accepted, my client plans to support me in publishing a "Partner Logos" plugin so the community can benefit from this.

[NateWr]

PR:

• pkp/pkp-lib#10521 Add hooks to extend Publisher Library categories #10522 (stable-3_3_0)

Tests:

• TESTS ONLY pkp/pkp-lib#10521 Add hooks to extend Publisher Library categories ojs#4470 (stable-3_3_0)

[NateWr]

It looks like the postgres tests are failing in a way that doesn't look likely to be related to this PR:

psql: error: connection to server on socket "/var/run/postgresql/.s.PGSQL.5432" failed: FATAL: Peer authentication failed for user "postgres"

[NateWr]

@asmecher Jonas re-ran the tests for me and they're still failing on a postgres connection error. It looks like all the pgsql tests failed in the last commit to stable-3_3_0 too, but not on this connection error: https://github.com/pkp/ojs/commits/stable-3_3_0/