Pin jupyter client < 8

[kevin-bates]

In toubleshooting #376, it was clear we need to pin (cap) the jupyter_client package < 8. This pull request also includes the following:

1. Adds a better default log format that includes color encodings and timestamps to the millisecond (same as JEG)
2. Adds the JKG version to the startup message (same as JEG)

$ jupyter kernelgateway --KernelGatewayApp.api=kernel_gateway.notebook_http --KernelGatewayApp.seed_uri=/Users/kbates/jkg-example.ipynb --port=10100       
[I 2023-02-06 10:49:34.739 KernelGatewayApp] Kernel started: 81225f93-44df-484c-89cb-96d0fbbc7c26, name: python3
[I 2023-02-06 10:49:35.647 KernelGatewayApp] Registering resource: /hello/world, methods: (['GET'])
[I 2023-02-06 10:49:35.647 KernelGatewayApp] Registering resource: /_api/spec/swagger.json, methods: (GET)
[I 2023-02-06 10:49:35.655 KernelGatewayApp] Jupyter Kernel Gateway 2.6.0.dev0 is available at http://127.0.0.1:10100

3. Removes Python 3.6 from the CI matrix and set of supported python versions.

[codecov]

Codecov Report

Base: 95.69% // Head: 95.69% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (fb34792) compared to base (c72803a).
Patch coverage: 83.33% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #378   +/-   ##
=======================================
  Coverage   95.69%   95.69%           
=======================================
  Files          31       31           
  Lines        2251     2255    +4     
=======================================
+ Hits         2154     2158    +4     
  Misses         97       97           

Impacted Files	Coverage Δ
kernel_gateway/tests/test_jupyter_websocket.py	99.45% <ø> (ø)
kernel_gateway/gatewayapp.py	84.21% <83.33%> (+0.22%)	⬆️

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