Walkthrough additions

[Yubo-Cao]

Closes Yubo-Cao#6

This PR fixes the following error:

1. IllegalStateException in search walkthrough
2. IndexOutOfBounds and cannot close database during DialogService.showAndWait in the add group walkthrough

Steps to test

1. The Search walkthrough should work properly even if multiple library tab is open
2. The Add Group walkthrough should be more robust to unwanted user interaction. Specifically, you may launch the add group walkthrough and:
   a. Click on other group in the entry tab during the walkthrough without leading to error
   b. Close the add group dialog in the middle without leading to error

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• I manually tested my changes in running JabRef (always required)
• [/] I added JUnit tests for changes (if applicable)
• [/] I added screenshots in the PR description (if change is visible to the user)
• [/] I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)
• I checked the user documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request updating file(s) in https://github.com/JabRef/user-documentation/tree/main/en.

[trag-bot]

Exception is used for control flow rather than an exceptional state. The code should handle the case where node cannot be positioned as a normal flow path instead of throwing an exception.

[Yubo-Cao]

The exception is intentional to catch programming error. A failed to detach state leads to undefined behavior—whether we should darken the entire window, or to highlight nothing, is questionable—but a sure way to lead to errors in subsequent calls to the Spotlight object.

[subhramit]

Thanks for quick action!

[subhramit]

For the submodules thing, see https://devdocs.jabref.org/code-howtos/faq.html#submodules

[Siedlerchr]

You just need to run the openrewrite task, then it will be good

[jabref-machine]

Note that your PR will not be reviewed/accepted until you have gone through the mandatory checks in the description and marked each of them them exactly in the format of [x] (done), [ ] (not done yet) or [/] (not applicable).