YAML file supporting extra json parameters for LocalFileSystemBackend

[VinayGb665]

LocalFileSystemBackend supports YAML files to add connections and the extra parameters ( like in here ) would have to be provided as raw JSON instead of default YAML. The PR is to resolve this issue and provide extra parameters as nested key pairs

Relevant to #9477
Make sure to mark the boxes below before creating PR: [x]

• Description above provides context of the change
• Unit tests coverage for changes (not needed for documentation changes)
• Target Github ISSUE in description if exists
• Commits follow "How to write a good git commit message"
• Relevant documentation is updated including usage instructions.
• I will engage committers as explained in Contribution Workflow Example.

---

In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.
Read the Pull Request Guidelines for more information.