Update e2e tests

[kaibocai]

This PR

1. fixes issues in current e2e tests

• removed incorrect assert, for ex

    expect(state?.serializedInput).toBeUndefined();
    expect(state?.serializedOutput).toBeUndefined();
    expect(state?.serializedCustomStatus).toBeUndefined();

serializedInput, serializedOutput and serializedCustomStatus will be '' instead of undefined

2. add more tests for new scenarios.

• single timer
• Fan-in/Fan-out

3. improve current tests for better readablity

• continue as new
• sub-orchestration

Currently two test cases are failing, both time out.

durabletask-js/test/e2e/orchestration.spec.ts

Line 145 in 0165d97

it("should be able to use the sub-orchestration for fan-out", async () => {

durabletask-js/test/e2e/orchestration.spec.ts

Line 325 in 0165d97

it("should allow to continue as new", async () => {

[kaibocai]

combined into PR #14