sngrep: add page (#11501)

Co-authored-by: Juri Dispan <juri.dispan@posteo.net>
Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

pages/common/sngrep.md

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+# sngrep
+
+> Tool for displaying SIP calls message flows from terminal.
+> More information: <https://github.com/irontec/sngrep>.
+
+- Visualize SIP packets from a PCAP file:
+
+`sngrep -I {{path/to/file.pcap}}`
+
+- Visualize only dialogs starting with INVITE packets with RTP packets from a PCAP file:
+
+`sngrep -crI {{path/to/file.pcap}}`
+
+- Real-time interface with only dialogs starting with INVITE packets with RTP packets:
+
+`sngrep -cr`
+
+- Only capture packets without interface to a file:
+
+`sngrep -NO {{path/to/file.pcap}}`