[stp] Cannot interop with stp because of not supporting config vlan1 in sonic

[yangjingming1]

As the title.
In PVST HLD（https://github.com/sonic-net/SONiC/blob/master/doc/stp/SONiC_PVST_HLD.md），it says “PVST+ support allows the device to interoperate with IEEE STP and also tunnel the PVST+ BPDUs transparently across IEEE STP region to potentially connect other PVST+ switches across the IEEE STP region. For interop with IEEE STP, PVST+ will send untagged IEEE BPDUs (MAC - 01:80:C2:00:00:00) with information corresponding to VLAN 1. The STP port must be a member of VLAN 1 for interoperating with IEEE STP.”

But in sonic，configuring vlan1 is not allowed.

So how can we support stp mode？

[azure-pipelines-wrapper]

Thanks for opening this issue!