feat(sdk-core): add externalSigner createOfflineRound1Share handler #2807

Job	Run time
Generate head API spec	7m 41s
Generate merge base API spec	8m 11s
Check specs identical	4s
API Spec Check	4s
Generate vacuum reports for API spec	0s
Check breaking changes	0s
Linter Override	0s
	16m 0s

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