Fix Instance-level Project Integration Management page for GitLab FOSS [RUN ALL RSPEC] [RUN-AS-IF-FOSS]

What does this MR do?

This MR fixes a bug where the Instance-level integrations table was not available for FOSS users. The table was updated to use Vue in !57198 (merged), and the JS was not included in the FOSS entry point.

This MR adds this inclusion, as well as a simple spec addition to test for the existence of the table.

Note: this MR has label Pick into 13.11

Related issue: #329165 (closed)

Resolves #262528 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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