Add topic filter for event WebSocket

[florian-h05]

Closes #4549.
Closes #3764.

The topic filter can be configured by sending a WS message like in following examples:

Only send all ItemCommandEvents:

{
  "type": "WebSocketEvent",
  "topic": "openhab/websocket/filter/topic",
  "payload": "[\"openhab/items/*/command\"]",
  "source": "ui-c2ead538aa"
}

Only send all ItemCommandEvents, except for the test Item:

{
  "type": "WebSocketEvent",
  "topic": "openhab/websocket/filter/topic",
  "payload": "[\"openhab/items/*/command\", \"!openhab/items/test/command\"]",
  "source": "ui-c2ead538aa"
}

Send all events, except ItemCommandEvents:

{
  "type": "WebSocketEvent",
  "topic": "openhab/websocket/filter/topic",
  "payload": "[\"!openhab/items/*/command\"]",
  "source": "ui-c2ead538aa"
}

[florian-h05]

@ghys We are getting close to have the event WS support everything we need in the UI 🚀

[spacemanspiff2007]

Would it be possible to provide a negative and positive filter here, too?
E.g. a filter that passes certain topics and a filter that rejects them?

[florian-h05]

Added just a few seconds ago 👍
See the PR description for how to use that.

[spacemanspiff2007]

Is the topic not a regular expression? Is it something openhab specific?

[florian-h05]

Topics can be defined as string with the * wildcard, see SSE events.
Internally, the topic expressions are converted to RegEx, during this conversion I can check whether the topic is to include or to ! exclude.

[spacemanspiff2007]

If you look at the /items endpoint some time ago there was a switch away from the openhab specific wildcard implementation to a regular expression.
Do you think it would make sense to use a normal regular expression here, too?

[florian-h05]

Do you think it would make sense to use a normal regular expression here, too?

I don‘t think that the additional regex features would be a benefit here, I think the wildcard is enough.

[spacemanspiff2007]

I don‘t think that the additional regex features would be a benefit here, I think the wildcard is enough.

But why use an custom openhab wildcard implementation which then gets internally converted into regex instead of just allowing a regex from the start instead?
This seems overly complicated and unnecessarily restrictive.

[florian-h05]

It makes the filters easier to use from clients though, as you can simply specify the topic with wildcards and don't need to take care of the RegEx.
The SSE event subscription is there since at least 2019 and since then no one ever asked for RegEx support for the topic filter.