feat: Implement initial Langflow Assistant API with streaming support (#11374)

* add agentic api backend

* [autofix.ci] apply automated fixes

* add docs to feature

* ruff and test fixes

* ruff fixes

* fix lfx tests

* fix ruff style

* [autofix.ci] apply automated fixes

* [autofix.ci] apply automated fixes (attempt 2/3)

* refactor code improvements

* add rate limit to tests

* [autofix.ci] apply automated fixes

* new canvas control

* add flow lock timeout

* [autofix.ci] apply automated fixes

* add more shards on pw tests

* Revert "new canvas control"

This reverts commit 9a266432b3c5720ac233425b7e471284c0642db2.

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Edwin Jose <edwin.jose@datastax.com>