release: Exclude not ready components from release

[Xuanwo]

As suggested by @wu-sheng:

Also, as other source codes are not ready, please exclude them from
the source tar.

ref: https://lists.apache.org/thread/57d2ysx96s5d0cmz07tdkprbvl45vx8y

[suyanhanx]

How about add the directory of unreleased components to .gitattributes as export-ignore?

[Xuanwo]

How about add the directory of unreleased components to .gitattributes as export-ignore?

Yes, this is exactly what I wanted.

[Xuanwo]

Components that we released include:

• core
• bindings/java
• bindings/python
• bindings/nodejs