TCAT TLS connection setup: inconsistent state

[EskoDijk]

Describe the bug
If a TCAT Commissioner connects via TLS, and the handshake succeeds, but the mTcatAgent.Connected(mTls) setup routine for the TCAT agent fails with an error, then the state becomes inconsistent: the Commissioner thinks it is successfully connected. The TCAT Device has its TLS connection established but TCAT Agent is inactive so won't process any commands.

To Reproduce
(No details given) Connect using a TCAT Commissioner certificate that would fails the checks in Error TcatAgent::Connected(MeshCoP::SecureTransport &aTlsContext) .

1. Git commit id: ee83d45
2. IEEE 802.15.4 hardware platform: simulation
3. Build steps: ./script/cmake-build simulation -DOT_FULL_LOGS=ON
4. Network topology: single simulated node

Expected behavior
Fate-sharing: if TCAT Device rejects the Commissioner, close the TLS, and send alert to Commissioner. Vice versa if Commissioner rejects the Device, send alert to Device (haven't checked that side yet).

Expect that the return status of this line is used:

            IgnoreReturnValue(mTcatAgent.Connected(mTls));

Console/log output
(TBD) I'll work on a first fix/PR of this issue in order to proceed with the work on TCAT certificates.

Additional context Add any other context about the problem here.
(TBD) I'll work on a first fix/PR of this issue in order to proceed with the work on TCAT certificates.