`Communication`: Add loading indicator when adding users to channel #12978

Job	Run time
get-labels	3s
check-build-status	3s
filter-matrix (artemis-test1.artemis.cit.tum.de, artemis-test1, https://artemis-test1.artemis.cit...	1s
filter-matrix (artemis-test2.artemis.cit.tum.de, artemis-test2, https://artemis-test2.artemis.cit...	1s
filter-matrix (artemis-test3.artemis.cit.tum.de, artemis-test3, https://artemis-test3.artemis.cit...	1s
filter-matrix (artemis-test4.artemis.cit.tum.de, artemis-test4, https://artemis-test4.artemis.cit...	1s
filter-matrix (artemis-test5.artemis.cit.tum.de, artemis-test5, https://artemis-test5.artemis.cit...	1s
filter-matrix (artemis-test6.artemis.cit.tum.de, artemis-test6, https://artemis-test6.artemis.cit...	1s
filter-matrix (artemis-test7.artemis.cit.tum.de, artemis-test7, https://artemis-test7.artemis.cit...	1s
filter-matrix (artemis-test9.artemis.cit.tum.de, artemis-test9, https://artemis-test9.artemis.cit...	1s
process-matrix	1s
deploy (artemis-test3.artemis.cit.tum.de, artemis-test3, https://artemis-test3.artemis.cit.tum.de...	20s
add-error-label	2s
	37s

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