Add Config::add_root_certificate for trusting custom ca #119

Job	Run time
Test Suite (stable)	1m 5s
Test Suite (network-enabled tests) (stable)	1m 2s
Check (stable)	26s
Test Suite (beta)	1m 11s
Lints (stable)	25s
Test Suite (network-enabled tests) (beta)	1m 6s
Check (beta)	35s
Test Suite (1.58.0)	2m 37s
Lints (beta)	45s
Test Suite (network-enabled tests) (1.58.0)	1m 19s
Check (1.58.0)	2m 38s
Test Suite (nightly, true)	1m 12s
Lints (1.58.0)	32s
Check (nightly, true)	31s
Test Suite (network-enabled tests) (nightly, true)	1m 9s
Lints (nightly, true)	27s
	17m 0s

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