Add dump for Vpn

Adding additional logging and dump information to help VPN debug.

Sample dump result(adb shell dumpsys vpn_management)

VPNs:
  0: com.vpn.test
    Active package name: com.vpn.test
    Active vpn type: 2
    NetworkCapabilities: [ Transports: VPN Capabilities: NOT_METERED&INTERNET&NOT_RESTRICTED&TRUSTED&NOT_VCN_MANAGED TransportInfo: <VpnTransportInfo{type=2, sessionId=null}> Uids: <{0-99999}> OwnerUid: 10106 AdminUids: [10106] UnderlyingNetworks: [107]]
    Token: 8876c2c4-df5f-46b8-82c7-8f124178254a
    MOBIKE enabled
    mUnderlyNetworkChanges (most recent first):
      2022-10-31T17:42:31.039068 - Switch to 107
      2022-10-31T17:42:29.510574 - Agent connect. Switch to 105
      2022-10-31T17:41:57.590691 - Agent connect. Switch to 103
      2022-10-31T17:41:31.269923 - Switch to 103
      2022-10-31T17:41:20.145050 - Switch to 102
      2022-10-31T17:41:14.480618 - Agent connect. Switch to 100
    mVpnManagerEvent (most recent first):
      2022-10-31T17:42:11.641201 - Event class=ERROR_CLASS_RECOVERABLE, err=ERROR_CODE_NETWORK_LOST for com.vpn.test on session 8876c2c4-df5f-46b8-82c7-8f124178254a
      2022-10-31T17:41:34.921219 - com.vpn.test stopped

Test: atest FrameworksNetTests
Test: adb shell dumpsys vpn_management
Bug: 238696406
Change-Id: I05b66ddb4a2b7a73707db39c6b89bf497aed1266