permissions: add backoffice readonly action and permission #1232

Job	Run time
Tests (circulation, 3.9, pypi, postgresql14, opensearch2)	8m 16s
Tests (ils, 3.9, pypi, postgresql14, opensearch2)	13m 17s
Tests (document_requests, 3.9, pypi, postgresql14, opensearch2)	3m 28s
Tests (acquisition, 3.9, pypi, postgresql14, opensearch2)	3m 2s
Tests (ill, 3.9, pypi, postgresql14, opensearch2)	4m 0s
	32m 3s

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