refactor: refactor is ready

[JoanFM]

Changes introduced
We are currently setting is_ready before the runtime is actually really ready to handle traffic. This PR gives the responsability to set is_ready flag to the runtime and tries to make sure that is_ready is more meaningful.

It also allows us to avoid the need to call terminate and have a potentially more grateful shutdown

[codecov]

Codecov Report

Merging #2833 (ca8d039) into master (0094bbf) will increase coverage by 6.88%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2833      +/-   ##
==========================================
+ Coverage   82.21%   89.10%   +6.88%     
==========================================
  Files         106      138      +32     
  Lines        7064     9371    +2307     
==========================================
+ Hits         5808     8350    +2542     
+ Misses       1256     1021     -235     

Flag	Coverage Δ
daemon	47.15% <ø> (?)
jina	88.50% <ø> (?)

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Impacted Files	Coverage Δ
jina/__init__.py	71.64% <ø> (ø)
jina/checker.py	96.55% <ø> (ø)
jina/clients/__init__.py	100.00% <ø> (ø)
jina/clients/base/__init__.py	90.90% <ø> (ø)
jina/clients/base/grpc.py	63.82% <ø> (ø)
jina/clients/base/http.py	93.02% <ø> (ø)
jina/clients/base/websocket.py	86.36% <ø> (ø)
jina/clients/grpc.py	100.00% <ø> (ø)
jina/clients/helper.py	100.00% <ø> (ø)
jina/clients/http.py	100.00% <ø> (ø)
... and 215 more

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[jacobowitz]

lgtm, we may add some wrapper later in the base runtime to hide the event implementation from the concrete runtimes, but that does not change too much.

[jacobowitz]

Actually there are some tests failing which look legit: https://github.com/jina-ai/jina/pull/2833/checks?check_run_id=2969742801