Split `amber` folder into `dashboard-service` and `workflow-execution-service` and do some renaming

### Task Summary

#### Background
There are several micro services under the project root, including:
- [access-control-service](https://github.com/apache/texera/tree/main/access-control-service)
- [computing-unit-managing-service](https://github.com/apache/texera/tree/main/computing-unit-managing-service)
- [config-service](https://github.com/apache/texera/tree/main/config-service)
- [file-service](https://github.com/apache/texera/tree/main/file-service)
- [workflow-compiling-service](https://github.com/apache/texera/tree/main/workflow-compiling-service)

Each folder contains one micro-service

However, [amber](https://github.com/apache/texera/tree/main/amber) contains two micro services, `TexeraWebApplication` and `WorkflowExecutionService`. We should separate these two services out as separate folders under the project root. After that, we should rename `TexeraWebApplication` to `TexeraDashboardService` to align the naming with other services

#### TODOs

1. Create `dashboard-service` folder and move the `TexeraWebApplication` related logic to there.
2. Create `execution-service` folder and move the `WorkflowExecutionService` related logic to there.
3. Rename `TexeraWebApplication` to `TexeraDashboardService`

### Priority

P1 – High

### Task Type

- [ ] Code Implementation
- [ ] Documentation
- [x] Refactor / Cleanup
- [ ] Testing / QA
- [ ] DevOps / Deployment

Start by inspecting the amber folder and the TexeraWebApplication and WorkflowExecutionService entry points to map each service's logic and references. Move the services into dashboard-service and execution-service, rename TexeraWebApplication to TexeraDashboardService, and run the project's available build or tests to verify references remain valid.

Written by the indexing model from the issue text.