Add OWNERS for each sub-project

[yizha1]

The OWNERS are admin maintainers who can update/delete sub-project and create security advisories.

See the definition of roles: Repository roles for an organization

See example, https://github.com/oras-project/oras/blob/main/OWNERS.md

[toddysm]

@yizha1 We already have the https://github.com/notaryproject/.github/blob/main/CODEOWNERS and https://github.com/notaryproject/.github/blob/main/MAINTAINERS files for that purpose. I don't think another file is required.

[SteveLasker]

Getting more clarity is great. This also affirms we need to document the expectations across the repos.
Please see: #16

[yizha1]

As clarified in another issue: CODWOWNERS and OWNERS are different.

• CODEOWNERS are clearly defined here https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
• OWNERS lists people with the Admin role, which is defined here https://docs.github.com/en/organizations/managing-user-access-to-your-organizations-repositories/repository-roles-for-an-organization#repository-roles-for-organizations.

OWNERS is just an arbitrary file name. Maintainers can have both Maintain and Admin roles. In this case, there is no need to create another file of OWNERS. We can update existing MAINTAINERS with the association of repository roles.

[toddysm]

Closing this one as per the discussion above. We don't need additional file for this information.