feat: register lease/cluster/maintanance grpc gateway handlers

[fengxsong]

Since APISIX had remove support for connecting to etcd via grpc connection, and for now apisix-ingress-controller adds an experimental feature that act as an etcd-adapter, when running in this mode, the following error will be reported in the APISIX gateway logs

2024/01/31 07:16:36 [error] 88#88: *1982 lua user thread aborted: runtime error: /usr/local/apisix/apisix/core/etcd.lua:336: attempt to index field 'body' (a nil value)
stack traceback:
coroutine 0:
	/usr/local/apisix/apisix/core/etcd.lua: in function 'set'
	/usr/local/apisix/apisix/plugins/server-info.lua:128: in function 'set'
	/usr/local/apisix/apisix/plugins/server-info.lua:192: in function 'report'
	/usr/local/apisix/apisix/plugins/server-info.lua:292: in function </usr/local/apisix/apisix/plugins/server-info.lua:287>
coroutine 1:
	[C]: in function 'thread_wait'
	/usr/local/apisix/apisix/timers.lua:52: in function </usr/local/apisix/apisix/timers.lua:32>
	[C]: in function 'pcall'
	/usr/local/apisix/apisix/core/timer.lua:40: in function </usr/local/apisix/apisix/core/timer.lua:36>
	[C]: in function 'pcall'
	/usr/local/apisix/apisix/core/timer.lua:63: in function </usr/local/apisix/apisix/core/timer.lua:56>, context: ngx.timer

Looking at the code of APISIX, it will try to request the Lease API of etcdserver.

So it seems that it's better to register the rest grpc gateway handlers as here. (at lease the LeaseHandler)

[CLAassistant]

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[fengxsong]

Related to apache/apisix-helm-chart#714