Enhancement: CLI Profiles Linux Support

[jakedoublev]

Background

Support was recently added to the otdfctl CLI tool to store authentication credentials (client creds or an access token from the PKCE auth code flow) in a profile on Mac OS/Windows.

We should support Linux as well.

Acceptance Criteria

1. Global config supports definition of a writable directory on the file system
2. CLI can fully CRUD profiles from that file system location instead of the keyring
3. e2e tests prove the behavior in CI and detect future regressions