chore: enable revive exported linter and add missing comments

[Mallikarjunadevops]

Addresses #8037 by enabling the exported rule for the revive linter in .golangci.yml and fixing the exposed undocumented exported identifiers across the jx repository.

Changes:

• Enabled exported rule for
  evive in .golangci.yml.
• Added missing comments in:
  • pkg/cmd/version/version.go
  • pkg/cmd/namespace/namespace.go
  • pkg/cmd/dashboard/dashboard.go
  • pkg/cmd/upgrade/upgrade.go, upgrade_cli.go, upgrade_plugins.go
  • pkg/plugins/helpers.go

Fixes: #8037

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