[BUG] Cannot add knowledges to Agent and "knowledge_sources" parameter doesnt work on Crew

### Description

The test code:
```
from crewai import Agent, Task, Crew, Process, LLM
from crewai.knowledge.source.string_knowledge_source import StringKnowledgeSource

# Create a knowledge source
content = "Users name is John. He is 30 years old and lives in San Francisco."
string_source = StringKnowledgeSource(
    content=content,
)

# Create an LLM with a temperature of 0 to ensure deterministic outputs
llm = LLM(model="gpt-4o", temperature=0)

# Create an agent with the knowledge store
agent = Agent(
    role="About User",
    goal="You know everything about the user.",
    backstory="""You are a master at understanding people and their preferences.""",
    verbose=True,
    allow_delegation=False,
    llm=llm,
    knowledge_sources=[string_source],
)
task = Task(
    description="Answer the following questions about the user: {question}",
    expected_output="An answer to the question.",
    agent=agent,
)

crew = Crew(
    agents=[agent],
    tasks=[task],
    verbose=True,
    process=Process.sequential,
    knowledge_sources=[string_source],
)

result = crew.kickoff(inputs={"question": "What city does John live in and how old is he?"})
```
Firstly, i use `knowledge_sources` on both Agent and Crew, but then i check my database, only knowledge of Crew is added to chromadb, Agent's knowledge isn't. So i check [set_knowledge](https://github.com/crewAIInc/crewAI/blob/cb1a98cabf1d62f4a1eff44fad364854c866d346/src/crewai/agent.py#L161) function in `agent.py` and added: `self.knowledge.add_sources()` , it works.
Secondly, if i only define `knowledge_sources` on Crew, the Agent actually doesnt get access to knowledge source. Continue checking, i realize that [in this logic](https://github.com/crewAIInc/crewAI/blob/cb1a98cabf1d62f4a1eff44fad364854c866d346/src/crewai/agent.py#L261), knowledge of Crew only add to `task_prompt` when knowledge of Agent exist. I thought if i define `knowledge_sources` on Crew level, all Agents will get access to the knowledge as well?
Are these bugs or what am i missing here?

### Steps to Reproduce

Run the test code

### Expected behavior

Knowledges of Agent should be added to database and `knowledge_sources` should work on Crew level

### Screenshots/Code snippets

Database's collection when run test code (Collection of Agent is empty):
```
Collection: knowledge_crew
{'ids': ['225f7a909030abdbcdd1f8d0657e0e5bcd64a725936f50246ec4ac28fcf4ffe9'], 'embeddings': None, 'documents': ['Users name is John. He is 30 years old and lives in San Francisco.'], 'uris': None, 'data': None, 'metadatas': [None], 'included': [<IncludeEnum.documents: 'documents'>, <IncludeEnum.metadatas: 'metadatas'>]}
Collection: knowledge_About_User
{'ids': [], 'embeddings': None, 'documents': [], 'uris': None, 'data': None, 'metadatas': [], 'included': [<IncludeEnum.documents: 'documents'>, <IncludeEnum.metadatas: 'metadatas'>]}
```


### Operating System

Ubuntu 20.04

### Python Version

3.12

### crewAI Version

0.119.0

### crewAI Tools Version

0.119.0

### Virtual Environment

Venv

### Evidence

None

### Possible Solution

None

### Additional context

None

Labels: bug, no-issue-activity
State: closed