[MWAN] Integration guide for Juniper Networks SRX Series Firewalls (#18320)

* added content

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* refined page

* added juniper to dev compat page

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Co-authored-by: hyperlint-ai[bot] <154288675+hyperlint-ai[bot]@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Pedro Sousa <[email protected]>

* separated keys in kbd

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Co-authored-by: hyperlint-ai[bot] <154288675+hyperlint-ai[bot]@users.noreply.github.com>
Co-authored-by: Pedro Sousa <[email protected]>

Author: 3 people