[Governance] Update community membership requirements

[hzxuzhonghu]

From the document https://github.com/volcano-sh/community/blob/master/community-membership.md

We can see

Role	Requirements	Responsibilities	Privileges
Member	Sponsor from 2 approvers, active in community, contributed to Volcano	Welcome and guide new contributors	Volcano GitHub organization Member
Reivewer	Sponsor from 2 maintainers, has basic experience and knowledge of domain, actively contributed to code and review	Review contributions from community members	Write access to specific packages in relevant repository
Approver	Sponsor from 2 maintainers, has good experience and knowledge of domain, actively contributed to code and review	Review and approve contributions from community members	Write access to specific packages in relevant repository
Maintainer	Sponsor from 2 owners, shown good technical judgement in feature design/development and PR review	Participate in release planning and feature development/maintenance	Top level write access to relevant repository. Name entry in Maintainers file of the repository
Owner	Sponsor from 3 owners, helps drive the overall Volcano project	Drive the overall technical roadmap of the project and set priorities of activities in release planning	Volcano GitHub organization Admin access

There is a owner role, which can not correctly reflect volcano's operation. We donot see owners' activity, and also can not know who are owners.

So if one want to apply to become maintainer, this current requirement can not be satisfied

Requirements
Sponsor from 2 owners
Approver for at least 2 months
Nominated by a project owner
Good technical judgement in feature design/development

I would suggest we deprecate owner role and update maintainer requirement to

Requirements
Sponsor from 2 maintainers
Approver for at least 2 months
Nominated by a project maintainer
Good technical judgement in architecture and evolution of volcano

[hzxuzhonghu]

@volcano-sh/volcano-maintainer please take a look, and click 👍 or 👎

[kevin-wangzefeng]

+1, this document is out of date, we need to fix it.

Maintainers are the de facto top governing body of our community. We never really implemented the "owner" role, and I don't think we really need it.

[william-wang]

+1, agree with it.