DOC: make warning on absent annex appear less like an error

[adswa]

I have reworded the warning and info messages related to adding siblings without an annex. Mostly, I've removed the word "failed". I've played around with "downgrading" the message from "warning" to "info", but I guess the color coding as a warning helps to not miss a problem should there ever be one. The text should make sure that this Warning is no need for worry if the remote is a pure Git remote.

I think its better than the previous messages, but I'm not yet 100% satisfied. Here is how the message looks like for the situation described in #4322

datalad siblings add --name bitbucket --url https://testing_ittacc@bitbucket.org/testing_ittacc/mydataset.git
[INFO   ] Could not enable annex remote bitbucket. This is expected if bitbucket is a pure Git remote, or happens if it is not accessible. 
[WARNING] Could not detect whether bitbucket carries an annex. If bitbucket is a pure Git remote, this is expected. Remote was marked by annex as annex-ignore. Edit .git/config to reset if you think that was done by mistake due to absent connection etc 
.: bitbucket(-) [https://testing_ittacc@bitbucket.org/testing_ittacc/mydataset.git (git)]

If anyone has other suggestions, please say so. :)

This fixes #4322

[codecov]

Codecov Report

Merging #4323 into master will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4323      +/-   ##
==========================================
+ Coverage   88.83%   88.87%   +0.04%     
==========================================
  Files         285      285              
  Lines       37457    37457              
==========================================
+ Hits        33275    33291      +16     
+ Misses       4182     4166      -16     

Impacted Files	Coverage Δ
datalad/distribution/siblings.py	76.27% <100.00%> (ø)
datalad/downloaders/tests/test_http.py	60.96% <0.00%> (+2.16%)	⬆️
datalad/downloaders/http.py	74.90% <0.00%> (+2.78%)	⬆️

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[kyleam]

Thanks, I agree that these are improvements.

I've played around with "downgrading" the message from "warning" to "info", but I guess the color coding as a warning helps to not miss a problem should there ever be one. The text should make sure that this Warning is no need for worry if the remote is a pure Git remote.

I have a slight preference for an info message here, but the tradeoff you're mentioning does sound like a valid reason to stick to the warning.

[adswa]

Thanks for the review, @kyleam! Let's go for a small improvement (wording) now, and for a more radical change (warning versus info) if rewording feels like it did not go far enough after a while.