pathd: add 'show sr-te pcep session json' support

pathd: add 'show sr-te pcep session json' support

Add support to dump sr-te pcep session in json output.

> ubuntu2204# show sr-te pcep session
> PCE q
>  PCE IP 192.0.2.40 port 4189
>  PCC IP 192.0.2.10 port 4189
>  PCC MSD 10
>  Session Status UP
>  Precedence 10, best candidate
>  Confidence normal
>  Timer: KeepAlive config 30, pce-negotiated 70
>  Timer: DeadTimer config 120, pce-negotiated 120
>  Timer: PcRequest 30
>  Timer: SessionTimeout Interval 30
>  Timer: Delegation Timeout 10
>  No TCP MD5 Auth
>  PCE SR Version draft07
>  Next PcReq ID 5
>  Next PLSP  ID 2
>  Connected for 171 seconds, since 2023-10-28 09:36:44 UTC
>  PCC Capabilities: [PCC Initiated LSPs] [Stateful PCE] [SR TE PST]
>  PCE Capabilities: [Stateful PCE] [SR TE PST]
>  PCEP Message Statistics
>                         Sent   Rcvd
>          Message Open:     2      1
>     Message KeepAlive:     1      6
>         Message PcReq:     4      0
>         Message PcRep:     0      0
>        Message Notify:     4      0
>         Message Error:     0      5
>         Message Close:     0      0
>        Message Report:     5      0
>        Message Update:     0      1
>      Message Initiate:     0      0
>      Message StartTls:     0      0
>     Message Erroneous:     0      0
>                 Total:    16     13
> PCEP Sessions => Configured 1 ; Connected 1
> ubuntu2204# show sr-te pcep session  json
> {
>   "pcepSessions":[
>     {
>       "pceName":"q",
>       "pceAddress":"192.0.2.40",
>       "pcePort":4189,
>       "pccAddress":"192.0.2.10",
>       "pccPort":4189,
>       "pccMsd":10,
>       "sessionStatus":"UP",
>       "bestMultiPce":true,
>       "precedence":10,
>       "confidence":"normal",
>       "keepaliveConfig":30,
>       "deadTimerConfig":120,
>       "pccPcepRequestTimerConfig":30,
>       "sessionTimeoutIntervalSec":30,
>       "delegationTimeout":10,
>       "tcpMd5Authentication":false,
>       "draft07":true,
>       "draft16AndRfc8408":false,
>       "nextPcRequestId":5,
>       "nextPLspId":2,
>       "sessionKeepalivePceNegotiatedSec":70,
>       "sessionDeadTimerPceNegotiatedSec":120,
>       "sessionConnectionDurationSec":177,
>       "sessionConnectionStartTimeUTC":"2023-10-28 09:36:44",
>       "pccCapabilities":" [PCC Initiated LSPs] [Stateful PCE] [SR TE PST]",
>       "pceCapabilities":" [Stateful PCE] [SR TE PST]",
>       "messageStatisticsReceived":{
>         "messageOpen":1,
>         "messageKeepalive":6,
>         "messagePcReq":0,
>         "messagePcRep":0,
>         "messageNotify":0,
>         "messageError":5,
>         "messageClose":0,
>         "messageReport":0,
>         "messageUpdate":1,
>         "messageInitiate":0,
>         "messageStartTls":0,
>         "messageErroneous":0,
>         "total":13
>       },
>       "messageStatisticsSent":{
>         "messageOpen":2,
>         "messageKeepalive":1,
>         "messagePcReq":4,
>         "messagePcRep":0,
>         "messageNotify":4,
>         "messageError":0,
>         "messageClose":0,
>         "messageReport":5,
>         "messageUpdate":0,
>         "messageInitiate":0,
>         "messageStartTls":0,
>         "messageErrneous":0,
>         "total":16
>       }
>     }
>   ],
>   "pcepSessionsConfigured":1,
>   "pcepSessionsConnected":1
> }

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>