Remove version python-3.7 from pyproject.toml, update lock

[Mr-Geekman]

Before submitting (must do checklist)

• Did you read the contribution guide?
• Did you update the docs? We use Numpy format for all the methods and classes.
• Did you write any new necessary tests?
• Did you update the CHANGELOG?

Proposed Changes

• Remove version python-3.7 from pyproject.toml
• Update poetry.lock
• Add poetry.toml into gitignore

Closing issues

[codecov-commenter]

Codecov Report

Merging #1183 (b4c8e11) into master (6a8e478) will decrease coverage by 18.53%.
The diff coverage is 93.75%.

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@@             Coverage Diff             @@
##           master    #1183       +/-   ##
===========================================
- Coverage   87.65%   69.13%   -18.53%     
===========================================
  Files         177      177               
  Lines       10380    10380               
===========================================
- Hits         9099     7176     -1923     
- Misses       1281     3204     +1923     

Impacted Files	Coverage Δ
etna/analysis/eda_utils.py	19.93% <0.00%> (-41.14%)	⬇️
etna/analysis/outliers/median_outliers.py	95.83% <100.00%> (ø)
etna/clustering/distances/euclidean_distance.py	73.68% <100.00%> (-21.06%)	⬇️
etna/datasets/tsdataset.py	73.73% <100.00%> (-18.98%)	⬇️
...mental/classification/feature_extraction/weasel.py	97.67% <100.00%> (ø)
etna/transforms/encoders/mean_segment_encoder.py	100.00% <100.00%> (ø)
etna/transforms/math/differencing.py	97.76% <100.00%> (ø)

... and 66 files with indirect coverage changes

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[alex-hse-repository]

Am I write that user should also install the correct version of sqlalchemy? Should't we inform him somehow about it?

[Mr-Geekman]

If he has incorrect version he will face some errors working with databases in optuna (it is optuna's problem, not ours).

[alex-hse-repository]

Will it be obvious that the problem is in sqlalchimy?