fix(topology): delete action should be available for custom targets

[tthvo]

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Fixes: #1251

Description of the change:

• Update the allowList and blockList to be more flexible based on the tree element.
• Added check for REALM annotation to ensure that only Custom Target is allowed to be deleted.

Motivation for the change:

See #1251

[andrewazores]

Looks like it worked - the deletion button appears again, and after clicking it I can see a request sent and success response from the server, and a "target lost" notification. However, the Topology view didn't update on the notification, so I had to navigate away and back to see the updated view state.

Seems like a separate bug, but worth noting. In testing cryostatio/cryostat#407 it looks like Agents deregistering also doesn't trigger Topology to update, so it could be a common root cause.

[andrewazores]

Bypassed the rule this time, but @tthvo please set up your GPG signature again with this email account :-)

[tthvo]

Ohh oops! That's odd. Somehow, the commit signature keep being not recognized again...I will check next time :D Thanks :)))