Getting or creating a named actor is a common pattern, however it is somewhat esoteric in how to achieve this. Add a utility function and test that it doesn't cause any scary error messages.
Actor.options(name="my_singleton", get_if_exists=True).remote(args)
This PR makes a number of major overhauls to the Ray core docs:
Add a key-concepts section for {Tasks, Actors, Objects, Placement Groups, Env Deps}.
Re-org the user guide to align with key concepts.
Rewrite the walkthrough to link to mini-walkthroughs in the key concept sections.
Minor tweaks and additional transition material.
Combine `ParsedRuntimeEnv` and `RuntimeEnv` into `ray.runtime.RuntimeEnv`, details: #21495
- The `new RuntimeEnv` includes all external interfaces of `ParsedRuntimeEnv` and `old RuntimeEnv`.
- The `new RuntimeEnv` will be exposed directly to the user.
- example:
```python
runtime_env = ray.runtime_env.RuntimeEnv(working_dir="s3://workding_dir.zip",
pip=["requests"],
java_jars=["s3://jar1.zip"],
java_jvm_options=["-Dxxx=xxx"])
```
