Add `newly_created` bool field to the `ThreadCreate` event (#3084) #1047

Job	Run time
Build docs	54s
Examples	3m 2s
Test (macOS)	1m 50s
Check minimal versions	1m 1s
MSRV	0s
Test (nightly)	1m 57s
Test (stable)	2m 32s
Test (beta)	2m 32s
Test (Windows)	5m 44s
Test (native-tls)	2m 11s
Test (no default features)	51s
Test (no cache)	2m 0s
Test (no gateway)	1m 36s
Test (unstable Discord API features)	2m 10s
Test (zlib compression)	1m 54s
Test (zstd compression)	1m 53s
Test (zlib and zstd compression)	2m 8s
Test (chrono, chrono)	56s
Test (unstable API + typesize, default unstable typesize, true)	1m 6s
Test (builder without model, builder, true)	46s
Test (unstable Discord API (no default features), unstable, true)	40s
	37m 43s

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