### Background
The main scope of this change is enhancing the system capability (by fixing bug, correcting execution behaviour) to allow for creating a graph with a loop, to allow the use case of block auto-generation agent.
### Changes 🏗️
* Main changes: Add block_autogen.py (block auto-generation agent graph example).
* Refactor on test boilerplate: introduced `util/test` for initiating a server, and waiting graph execution.
* Removing unnecessary db lookup and duplicated codes used for sending execution updates on agent executor.
* Removed redundant code on test and cli code.
* Moved block test execution helper into the main code (so blockinstallerblock can use it).
* Eliminate the need of explicitly add a module into the `AVAILABLE_BLOCKS` list, any block class under the `block` folder will be auto-discovered.
* Few patches on the existing blocks.
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