permissions: add backoffice readonly action and permission #1237

Job	Run time
Tests (acquisition, 3.9, pypi, postgresql14, opensearch2)	2m 39s
Tests (document_requests, 3.9, pypi, postgresql14, opensearch2)	3m 11s
Tests (ils, 3.9, pypi, postgresql14, opensearch2)	13m 42s
Tests (circulation, 3.9, pypi, postgresql14, opensearch2)	7m 49s
Tests (ill, 3.9, pypi, postgresql14, opensearch2)	4m 12s
	31m 33s

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