docs: improve Secret Management section

[anakin87]

I have noticed on some online examples that some users struggle to understand how our Secret Management works.
#1 #2

I think that our docs should begin with one of two simple practical usage examples (useful for ordinary users), before going deep into explaining the implementation.

[srini047]

@anakin87 I would like to take up this issue.
A pipeline similar to this: https://github.com/LLM-Projects/haystack-book/blob/main/chapter-4/haystack_monitoring_prompt_injection.ipynb.

[anakin87]

@srini047 it is unrelated, sorry.

I simply mean showing an example like this:

works, but not serializable
generator = OpenAIGenerator(api_key=Secret.from_token("<your-api-key>"))

serializable, preferred way

# export an env var called OPENAI_API_KEY containing the API key
generator = OpenAIGenerator() #using the default env var for the component

serializable, with a custom env var

# export an env var called YOUR_ENV_VAR containing the API key
generator = OpenAIGenerator(api_key=Secret.from_env("YOUR_ENV_VAR"))

[srini047]

I actually thought an example as a pipeline. I can implement this and looks much simpler.

[srini047]

@anakin87 Suggested the changes through dash.readme.com.
Looking forward to take it from there.

[anakin87]

@dfokina please have a look when you can.

[dfokina]

Thank you @srini047 ! I just tweaked the text a little bit, and just published the suggestions.