Add switch channel commands into activationEvents

[formulahendry]

I see some users want to switch daily channel for new features (e.g. Jupyter Notebook native support), but meet with errors: command 'Python.swichToDailyChannel' not found.
So we need to add switch channel commands into activationEvents to avoid this kind of issues.

[codecov-io]

Codecov Report

Merging #7635 into master will decrease coverage by 0.68%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #7635      +/-   ##
=========================================
- Coverage   58.69%     58%   -0.69%     
=========================================
  Files         493     493              
  Lines       21995   21640     -355     
  Branches     3533    3528       -5     
=========================================
- Hits        12909   12552     -357     
- Misses       8278    8280       +2     
  Partials      808     808

Impacted Files	Coverage Δ
...nt/datascience/jupyter/invalidNotebookFileError.ts	0% <0%> (-75%)	⬇️
.../client/datascience/jupyter/jupyterConnectError.ts	0% <0%> (-66.67%)	⬇️
...science/jupyter/jupyterKernelPromiseFailedError.ts	0% <0%> (-50%)	⬇️
...ent/datascience/jupyter/jupyterWaitForIdleError.ts	0% <0%> (-50%)	⬇️
src/client/language/characters.ts	12% <0%> (-21.34%)	⬇️
src/client/testing/codeLenses/main.ts	60% <0%> (-17.78%)	⬇️
src/client/datascience/cellFactory.ts	72.34% <0%> (-17.32%)	⬇️
src/client/constants.ts	75% <0%> (-5%)	⬇️
src/client/providers/providerUtilities.ts	84.61% <0%> (-4.28%)	⬇️
src/client/api.ts	90% <0%> (-2.86%)	⬇️
... and 24 more

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[karrtikr]

Couldn't harm to add that, thanks @formulahendry .