Ftr: experimentally distributed transaction based on seata-golang

[dk-lockdown]

What this PR does:
support distributed transaction, by experimentally seata-golang

Special notes for your reviewer:
this pr just added a filter, to receive xid from attachments

[AlexStocks]

@dk-lockdown pls check the travis failure.

[Patrick0308]

I have a question, can be used filter with grpc or rest when another server which is not a dubbo server invoke our service.

[zouyx]

Can you provide a sample for this pr？

You can commit to the resposity as below

https://github.com/dubbogo/dubbo-samples

[dk-lockdown]

Can you provide a sample for this pr？

You can commit to the resposity as below

https://github.com/dubbogo/dubbo-samples

samples 我写了准备提交到一个地方，但是我看了看，如果提交到 https://github.com/dubbogo/dubbo-samples ，ci 会过不了，因为这个还要和 tc server 端配合使用，并且还需要和数据库交互

[dk-lockdown]

I have a question, can be used filter with grpc or rest when another server which is not a dubbo server invoke our service.

should work

[zouyx]

Can you provide a sample for this pr？
You can commit to the resposity as below
https://github.com/dubbogo/dubbo-samples

samples 我写了准备提交到一个地方，但是我看了看，如果提交到 https://github.com/dubbogo/dubbo-samples ，ci 会过不了，因为这个还要和 tc server 端配合使用，并且还需要和数据库交互

It's ok,you can ignore travis CI in this project.But you must promise your sample must work. Don'f forget write READEME.md

[dk-lockdown]

Can you provide a sample for this pr？
You can commit to the resposity as below
https://github.com/dubbogo/dubbo-samples

samples 我写了准备提交到一个地方，但是我看了看，如果提交到 https://github.com/dubbogo/dubbo-samples ，ci 会过不了，因为这个还要和 tc server 端配合使用，并且还需要和数据库交互

It's ok,you can ignore travis CI in this project.But you must promise your sample must work. Don'f forget write a READEME.md

好的，写了 readme.md 的

[zouyx]

i have no question.Wait for our next version please.

[fangyincheng]

LGTM