Update rules-engine-matching-conditions.rst

[cmillane]

Added a section on new Routing Key matching functionality, cleaned up some miscellaneous language, and added a section on rule processing order

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I added a section on new Routing Key matching functionality, cleaned up some miscellaneous language, and added a section on rule processing order

Enter a description of the changes, why they're good for the Observability Cloud documentation, and so on.

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[cmillane]

Hi @johannahp-splunk and @sheilattran8, thanks for reviewing my changes!
I'm hoping to merge this request to make the updates live. Do either of you happen to know if any further action is required from my side?

[jcatera-splunk]

Approving this to get all of our PR changes into our new docs before this repo is archived at the end of the month.