adi: ad5706r: Add support for ad5706r

[SaikiranGudla]

1. Add driver for ad5706r
2. Add example script for data streaming.
3. Update index.rst and Contents.m files.

Pull Request Description

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PR Type

• Bug fix (change that fixes an issue)
• New feature (change that adds new functionality)
• Breaking change (has dependencies in other repos or will cause CI to fail)

PR Checklist

• I have performed a self-review of the changes
• I have commented my code, at least hard-to-understand parts
• I have build all projects affected by the changes in this PR
• I have tested in hardware affected projects, at the relevant boards
• I have signed off all commits from this PR
• I have updated the documentation by running /docs/source/reference_api/gen_sysobj_doc.m script locally, if applies.