src/vs/platform/userDataSync/common/userDataSyncStoreService.ts/UserDataSyncStoreClient/createCollection
class UserDataSyncStoreClient:	async createCollection(headers: IHeaders = {}): Promise<string> {
		if (!this.userDataSyncStoreUrl) {
			throw new Error('No settings sync store url configured.');
		}

		const url = joinPath(this.userDataSyncStoreUrl, 'collection').toString();
		headers = { ...headers };
		headers['Content-Type'] = Mimes.text;

		const context = await this.request(url, { type: 'POST', headers }, [], CancellationToken.None);
		const collectionId = await asTextOrError(context);
		if (!collectionId) {
			throw new UserDataSyncStoreError('Server did not return the collection id', url, UserDataSyncErrorCode.NoCollection, context.res.statusCode, context.res.headers[HEADER_OPERATION_ID]);
		}
		return collectionId;
	}