Add an on/off knob for BGP EOIU pulling on warm restart

[heidinet2007]

Add a knob to turn on/off the BGP EOIU pulling when BGP warm restart. By default, it's off.
This is to address review comments for sonic-net/sonic-buildimage#2823

Other related PR

sonic-net/sonic-buildimage#3489

sonic-net/sonic-buildimage#2823
sonic-net/sonic-swss-common#273
sonic-net/sonic-swss#856

root@ASW-7001:~# config warm_restart bgp_eoiu true
root@ASW-7001:~# show warm_restart config 
name    enable    timer_name    timer_duration    eoiu_enable
------  --------  ------------  ----------------  -------------
bgp     false     NULL          NULL              true

root@ASW-7001:~# config warm_restart bgp_eoiu false
root@ASW-7001:~# show warm_restart config 
name    enable    timer_name    timer_duration    eoiu_enable
------  --------  ------------  ----------------  -------------
bgp     false     NULL           NULL             false


root@ASW-7001:~# config warm_restart bgp_timer 120
root@ASW-7001:~# show warm_restart config 
name    enable    timer_name      timer_duration  eoiu_enable
------  --------  ------------  ----------------  -------------
bgp     false     bgp_timer     120               false


root@ASW-7001:~# config warm_restart bgp_eoiu true
root@ASW-7001:~# show warm_restart config 
name    enable    timer_name      timer_duration  eoiu_enable
------  --------  ------------  ----------------  -------------
bgp      false    bgp_timer     120               true

[pavel-shirshov]

I'm ok if Joe approved it. I'm not an expert in this library

[pavel-shirshov]

retest this please

[yxieca]

retest this please