Add sli.do short link redirect (#4419) #3256

Job	Run time
Check backend needs building	9s
Check frontend needs building	13s
Check pretix needs building	16s
Build backend	0s
Deploy backend	34s
Build pretix	0s
Wait backend deployment	9s
Build frontend / Build	6m 10s
Deploy frontend	44s
Wait frontend deployment	1m 19s
	9m 34s

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