Blog post on query cancellation (#75)

* First draft

* Corrections based on feedback so far

* Add front matter and ASF header

* Integrating feedback from @alamb

* Add short inline comments

* Add `Acknowledgement` and `About DataFusion` sections

* Add images

* wordsmithing

* wordsmith and format

* Prettier images. Text revisions.

* Another round of proofreading by AI

* Obession: Wordsmithing for concision

* Update content/blog/2025-06-30-cancellation.md

* Update content/blog/2025-06-30-cancellation.md

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Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: pepijnve