use cmd context in sparkctl

[nabuskey]

Purpose of this PR

Currently, sparkctl uses context.Todo whenever it talks to k8s api. It's usually a better idea to create a context for cobra, then use it for subcommand executions. This will allow for a bit more complex things in the future like command timeout.

• Create a root context in the root command.
• In subcommands, retrieve the context through Cobra's cmd.Context(). Then use it for the rest of execution processes.

Change Category

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

Checklist

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

[ChenYi015]

/lgtm

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ChenYi015

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [ChenYi015]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment