feat: add switch interface BGP established metric

[mwennrich]

adds metal_switch_interface_bgp_established metric

# HELP metal_switch_interface_bgp_established_timestamp Provide the unix timestamp since BGP is established on the interfaces (0 if not established)
# TYPE metal_switch_interface_bgp_established_timestamp gauge
metal_switch_interface_bgp_established_timestamp{device="Ethernet0",machineid="00000000-0000-0000-0000-ac1f6b7d7efa",partition="fra-equ01",switchname="fra-equ01-r02leaf01"} 1.730715363e+09
metal_switch_interface_bgp_established_timestamp{device="Ethernet0",machineid="00000000-0000-0000-0000-ac1f6b7d7efa",partition="fra-equ01",switchname="fra-equ01-r02leaf02"} 1.730715441e+09
metal_switch_interface_bgp_established_timestamp{device="Ethernet1",machineid="00000000-0000-0000-0000-ac1f6b7d7e32",partition="fra-equ01",switchname="fra-equ01-r02leaf01"} 1.730715363e+09
metal_switch_interface_bgp_established_timestamp{device="Ethernet1",machineid="00000000-0000-0000-0000-ac1f6b7d7e32",partition="fra-equ01",switchname="fra-equ01-r02leaf02"} 1.730715441e+09
metal_switch_interface_bgp_established_timestamp{device="Ethernet2",machineid="00000000-0000-0000-0000-ac1f6b7d7dc6",partition="fra-equ01",switchname="fra-equ01-r02leaf01"} 0
metal_switch_interface_bgp_established_timestamp{device="Ethernet2",machineid="00000000-0000-0000-0000-ac1f6b7d7dc6",partition="fra-equ01",switchname="fra-equ01-r02leaf02"} 1.731591734e+09

References

References:

• feat: add support for reporting of switch BGP states by metal-core metal-api#598