Ftr: AccessLogFilter support

[flycash]

What this PR does:
Add AccessLogFilter

Which issue(s) this PR fixes:
Ftr: AccessLogFilter support

Fixes #

Special notes for your reviewer:
Please review the code about channel and file operation carefully. I'm new to Golang.

Does this PR introduce a user-facing change?:

[codecov-io]

Codecov Report

Merging #214 into develop will increase coverage by 0.81%.
The diff coverage is 72.8%.

@@             Coverage Diff             @@
##           develop     #214      +/-   ##
===========================================
+ Coverage    65.16%   65.98%   +0.81%     
===========================================
  Files           94       95       +1     
  Lines         6399     6511     +112     
===========================================
+ Hits          4170     4296     +126     
+ Misses        1792     1774      -18     
- Partials       437      441       +4

Impacted Files	Coverage Δ
config/service_config.go	65.51% <100%> (+0.4%)	⬆️
protocol/dubbo/listener.go	64.88% <100%> (+14.88%)	⬆️
filter/impl/access_log_filter.go	71.02% <71.02%> (ø)
cluster/cluster_impl/base_cluster_invoker.go	54.71% <0%> (-16.99%)	⬇️
filter/impl/hystrix_filter.go	68.64% <0%> (-3.39%)	⬇️
protocol/dubbo/readwriter.go	70.37% <0%> (+2.46%)	⬆️
protocol/dubbo/codec.go	82.35% <0%> (+5.88%)	⬆️
protocol/dubbo/pool.go	73.6% <0%> (+15.73%)	⬆️

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[hxmhlt]

LGTM

[fangyincheng]

Do you test in the examples for your feature?

[fangyincheng]

How to start this filter？

[flycash]

Now I add the example in general/go-server.
It looks like that:

and clients need to do nothing

[AlexStocks]

@fangyincheng should the examples be placed in dubbogo-examples?

[flycash]

I change the example to be comments:

It would be better.

[fangyincheng]

@fangyincheng should the examples be placed in dubbogo-examples?

yes

[fangyincheng]

I change the example to be comments:

It would be better.

Should it be default or user configuration? What about Java dubbo? And should you add some comments in access_log_filter.go instead of examples?

[flycash]

It's a default filter in Java. But if the user does not specify the value of "accesslog" to store the access log. It won't do anything.
So, maybe we could make it as default filter. But if the user doesn't configure the of "accesslog", we do nothing.

[fangyincheng]

It's a default filter in Java. But if the user does not specify the value of "accesslog" to store the access log. It won't do anything.
So, maybe we could make it as default filter. But if the user doesn't configure the of "accesslog", we do nothing.

you are right. Pls do it.

[flycash]

done, pls review that

[AlexStocks]

LGTM

[AlexStocks]

@fangyincheng u recheck it and merge it, pls.

[fangyincheng]

LGTM