Feat: no downtime reindex, second attempt

[David-Guillot]

Fixes #2

Hi @qcoumes ,

This PR supersedes #23 in my attempts to implement #2 . This is a very different approach, based on the Document class much more than on Index class:

• It simply allows a Document subclass to have multiple indices, by leveraging the ability of opensearch_dsl Document class to do so
• As far as the management command is concerned, the interface almost stays the same: obviously index rebuild was removed because it was not making any sense anymore, and document migrate has been added, but it doesn't do anything more than switching an alias (you need to call index create then document index to actually put documents into your new index)
• The issue of existing concrete index was solved: index create is working, as well as document migrate, which delete the concrete index if it exists

I'll let you judge if this architecture fits your vision of this lib. If it doesn't, I'll stop trying to implement #2 because it's been a lot of energy on my end, and if it needs another rewrite I'll just find a way to integrate this solution somewhere in our codebase, as an extension of this lib.

[codecov-commenter]

Codecov Report

Merging #37 (de27e73) into master (fe1a773) will decrease coverage by 1.40%. The diff coverage is 95.94%.

:mega: This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
- Coverage   95.65%   94.26%   -1.40%     
==========================================
  Files          12       12              
  Lines         576      628      +52     
  Branches       80       92      +12     
==========================================
+ Hits          551      592      +41     
- Misses         21       30       +9     
- Partials        4        6       +2     

Impacted Files	Coverage Δ
django_opensearch_dsl/documents.py	96.52% <93.75%> (-1.54%)	:arrow_down:
...o_opensearch_dsl/management/commands/opensearch.py	94.02% <100.00%> (-5.98%)	:arrow_down:
django_opensearch_dsl/management/enums.py	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[David-Guillot]

@qcoumes did you have some time to think about this?

[qcoumes]

Sorry, had a lot of work last month, I'll look at this tomorrow

[David-Guillot]

this feature will not be released immediately if you're OK with it.

Of course I'm okay with this, we're already relying on our fork's branch to benefit from this feature, we can continue doing so for a couple of months.