Drawer - Glass style follow up

[nicolethoen]

Add isGlass modifier as follow up to patternfly/patternfly#8103

DrawerPanelContent currently has a 'no-background' colorVariant which adds 'pf-m-no-background'.
We need to determine this prop's relationship to pf-m-plain. Do we want to stay consistent?

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Jira Issue: PF-3731

[coderabbitai]

⚠️ Possible Duplicate Issue(s)

• Drawer - add no-glass panel variant #12121

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[kmcfaul]

• add isPlain (isPlain = false should set no-plain modifier). isPlain should work with colorVariant - colorVariant should have priority if set.
• deprecate colorVariant value - no-background (internally use plain modifier)

story points - 5