adding get_query_function

[cedricboudinet]

Hello
Here is a PR adding a function enabling one to read the modbus function of a query.
It can be useful for modbus server development.
If you are ok with it I can complete the docs as well.
Bests
Cedric

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Cedric Boudinet.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email [email protected]
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails

[cla-bot]

We require contributors to sign our Contributor License Agreement. In order for us to review and merge your code, please fill https://forms.gle/5635zjphDo5JEJQSA to get added. Your document will be manually checked by the maintainer. Be patient...

[mhei]

Usually open source development works that way, that you create a full PR, i.e. including documentation etc.
In your documentation, I would for example expect to find a description of your use case for this new function - at the moment, you only described it roughly.

[cla-bot]

We require contributors to sign our Contributor License Agreement. In order for us to review and merge your code, please fill https://forms.gle/5635zjphDo5JEJQSA to get added. Your document will be manually checked by the maintainer. Be patient...

[cla-bot]

We require contributors to sign our Contributor License Agreement. In order for us to review and merge your code, please fill https://forms.gle/5635zjphDo5JEJQSA to get added. Your document will be manually checked by the maintainer. Be patient...

[cedricboudinet]

Dear @stephane
Could this PR be merged as well?
Bests
Cedric