Docs: Clarify that masking in Connection 'extra' JSON is keyword-dependent

[varaprasadregani]

Description

This PR updates the Masking Sensitive Data documentation to clarify that keys in a Connection's extra JSON field are not masked automatically unless they contain specific sensitive keywords.

Reason for Change:
Currently, the documentation states: "Airflow will by default mask Connection passwords and keys from a Connection’s extra (JSON) field..."
This implies that all keys in the extra field are masked by default, which is misleading. In reality, masking is triggered only if the key name contains a substring from the default sensitive keyword list (e.g., password, secret, token).

Changes in this PR:

1. Updated Default Masking Text: Explicitly states that masking depends on the key name containing a sensitive keyword.
2. Added Keyword List: Explicitly lists the default keywords (access_token, api_key, passphrase, etc.) so users know exactly what triggers the masking.
3. Added Examples Table: Added a table demonstrating the masking behavior across different scopes (Logs, UI, Rendered Templates) to differentiate between Connection extra JSON behavior and Variable behavior.

closes: #58514

[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.