Allow using kwargs in CLI

[ahuang11]

Closes #784

Allows setting kwargs like:
lumen-ai serve nino_ml.csv --agents sql hvplot --provider openai

Rendered output:

import lumen.ai as lmai
from lumen.sources.duckdb import DuckDBSource

from lumen.ai.agents import SQLAgent
from lumen.ai.agents import hvPlotAgent

llm = lmai.llm.OpenAI(
    api_key='sk-<redacted>'
)
cs = lmai.memory["current_source"] = DuckDBSource(
    tables=['nino_ml.csv'],
    uri=":memory:",
    initializers=["INSTALL httpfs;", "LOAD httpfs;"]
)

assistant = lmai.ExplorerUI(
    llm=llm,
    agents=[SQLAgent, hvPlotAgent]
)
assistant.servable("Lumen.ai")

Also renames base_url and azure_endpoint to provider_endpoint

[codecov]

Codecov Report

Attention: Patch coverage is 6.52174% with 86 lines in your changes missing coverage. Please review.

Project coverage is 60.58%. Comparing base (2c83a1b) to head (0fbdc56).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
lumen/command/ai.py	0.00%	82 Missing ⚠️
lumen/ai/llm.py	42.85%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #787      +/-   ##
==========================================
- Coverage   60.98%   60.58%   -0.40%     
==========================================
  Files         103      103              
  Lines       12544    12628      +84     
==========================================
+ Hits         7650     7651       +1     
- Misses       4894     4977      +83     

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