[Observability & Debuggability] Improve TCP, Beats & Elastic Agent inputs

[lucabelluccini]

• Histograms of number of open connections on common inputs (Beats already has some stats about connections peak & current), connection durations
• Counter of number of unexpected disconnections, etc…
• Size of incoming request sizes and/or status of the buffers (if available with little or no overhead), eventually including histograms
• Ability to enable a “audit/access mode” to know which agents target which LS instance
• Ability to enable "wireshark/hex mode" to enable as applicative dump of incoming data from TCP based inputs
• Add a counter to track the batches too large for the pre-allocated memory pool #515