[BUG] parse of BUILD_INFO failed if not set

[vsantele]

Describe the bug
With a fresh environment on my computer, my flow raises an error with the tool promptflow_vectordb.tool.common_index_lookup.search.
The function _get_custom_dimensions inside promptflow_vectordb\tool\common_index_lookup.py cannot get a build_number because the environment variable BUILD_INFO is not set.

How To Reproduce the bug
Steps to reproduce the behavior, how frequent can you experience the bug:

1. Create a conda environment with python=3.11
2. Install the lastest version of promptflow (1.16.1), promptflow-tools (1.4.0) and promptflow-vectordb (0.2.13)
3. Create a flow using promptflow_vectordb.tool.common_index_lookup.search with a FAISS index from Azure ML (I didn't test with other options)
4. Run the flow

Expected behavior
The index lookup has to work without the BUILD_INFO. It has to have fallback build_number if the environment variable is not set.

Running Information(please complete the following information):

• Promptflow Package Version using pf -v:

{
  "promptflow": "1.16.1",
  "promptflow-azure": "1.16.1",
  "promptflow-core": "1.16.1",
  "promptflow-devkit": "1.16.1",
  "promptflow-tracing": "1.16.1"
}
promtflow-vectordb===0.2.13
promptflow-tools===1.4.0

• Operating System: Windows 11
• Python Version using python --version: python==3.11.10

Additional context
There are discussions at #3632 with this error, but it was not the main topic and the issue is closed.

[ferronsw]

The requirement of this ENV should be documented or made optional.
I've spend to many hours on finding this problem. I think many others with me.