Use current context for validation functions

[Dohbedoh]

Following #746. Using the context is useful in CloudBees plugin that allow managing Kubernetes Cloud within folders.

cc @Vlatombe @jglick

Testing done

• Tested creation of new cloud under Manage Jenkins > Cloud
• Tested configuration of new cloud under Manage Jenkins > Cloud
• Tested creation of new Kubernetes Shared Cloud in a folder (CloudBees instance)
• Tested configuration of new Kubernetes Shared Cloud in a folder (CloudBees instance)

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[Dohbedoh]

@Vlatombe I could not find the reason for a requirement for Jenkins.ADMINISTER instead of Jenkins.MANAGE here. Seems to me that Jenkins.MANAGE is restrictive enough ?

[jglick]

MANAGE does not give you permission to configure clouds.

[Vlatombe]

Indeed, this line should be reverted.

[Dohbedoh]

@jglick @Vlatombe after digging a bit about this, the remaining Overall/Administer checks were added in #1580 but apparently we ought to allow users with Overall/Manage since #1546.

[Vlatombe]

#1546 is about letting Managers manage pod templates, but we don't let them edit other Kubernetes cloud configurations.

[jglick]

In general, users with only Manage cannot configure Jenkins.clouds.

[Dohbedoh]

But per #1546 it looks like we only check on the Manage permissions. The only reason this is still guarded by Overall/Administer is because core does not allow non admins to access the Cloud configuration page.
In anyway, I am following your recommendation here, and changing to Overall/Administer