Refactor websocket code to $oh namespace

[florian-h05]

This refactors the WebSocket connection code from #2884 to the $oh namespace,
same as it is for the SSE logic.

[florian-h05]

@ghys This refactors the WS to the $oh namespace.
Let's postpone merging this after the release to not impose any risks.

[relativeci]

#2570 Bundle Size — 10.9MiB (~+0.01%).

ad25fa0(current) vs 511b949 main#2569(baseline)

Warning

Bundle contains 2 duplicate packages – View duplicate packages

Bundle metrics   3 changes 1 regression

	Current #2570	Baseline #2569
Initial JS	1.92MiB(+0.08%)	1.92MiB
Initial CSS	577.83KiB	577.83KiB
Cache Invalidation	17.65%	17.83%
Chunks	226	226
Assets	249	249
Modules	2948(+0.03%)	2947
Duplicate Modules	152	152
Duplicate Code	1.8%	1.8%
Packages	96	96
Duplicate Packages	2	2

Bundle size by type   1 change 1 regression

	Current #2570	Baseline #2569
JS	9.11MiB (+0.01%)	9.11MiB
CSS	866.74KiB	866.74KiB
Fonts	526.1KiB	526.1KiB
Media	295.6KiB	295.6KiB
IMG	140.74KiB	140.74KiB
HTML	1.38KiB	1.38KiB
Other	871B	871B

Bundle analysis report Branch florian-h05:ws-rfc Project dashboard

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[florian-h05]

@ghys Can you please have a look at this PR?

[ghys]

It's good but I'd still prefer the access token to be passed in headers instead of the URL query: openhab/openhab-core#4490
(at least when possible)

This reduces the odds that it could appear in a log.
Even if ephemeral, tokens should never be logged.

If it's urgent please merge but otherwise I don't see why the rush.