[AIRFLOW-7076] Add support for HashiCorp Vault as Secrets Backend

[kaxil]

Add support for HashiCorp Vault as Secret Backend

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Issue link: AIRFLOW-7076

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[kaxil]

cc @dstandish

[codecov-io]

Codecov Report

Merging #7741 into master will decrease coverage by 0.84%.
The diff coverage is 65.43%.

@@            Coverage Diff             @@
##           master    #7741      +/-   ##
==========================================
- Coverage   86.96%   86.11%   -0.85%     
==========================================
  Files         920      921       +1     
  Lines       44436    44468      +32     
==========================================
- Hits        38644    38295     -349     
- Misses       5792     6173     +381     

Impacted Files	Coverage Δ
airflow/secrets/__init__.py	97.67% <ø> (ø)
airflow/providers/hashicorp/secrets/vault.py	65.43% <65.43%> (ø)
...flow/providers/apache/cassandra/hooks/cassandra.py	21.51% <0.00%> (-72.16%)	⬇️
...w/providers/apache/hive/operators/mysql_to_hive.py	35.84% <0.00%> (-64.16%)	⬇️
airflow/kubernetes/volume_mount.py	44.44% <0.00%> (-55.56%)	⬇️
airflow/providers/postgres/operators/postgres.py	50.00% <0.00%> (-50.00%)	⬇️
airflow/providers/redis/operators/redis_publish.py	50.00% <0.00%> (-50.00%)	⬇️
airflow/kubernetes/volume.py	52.94% <0.00%> (-47.06%)	⬇️
airflow/providers/mongo/sensors/mongo.py	53.33% <0.00%> (-46.67%)	⬇️
airflow/kubernetes/pod_launcher.py	47.18% <0.00%> (-45.08%)	⬇️
... and 39 more

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[dephusluke]

@kaxil you added airflow/providers/hashicorp/secrets/vault.py
say that in future there will be a HashicorpVaultHook. Where would that go?
https://issues.apache.org/jira/browse/AIRFLOW-3669

Maybe I'm getting this wrong but I thought the providers package is for hooks/operators/sensor ?

[kaxil]

@kaxil you added airflow/providers/hashicorp/secrets/vault.py
say that in future there will be a HashicorpVaultHook. Where would that go?
https://issues.apache.org/jira/browse/AIRFLOW-3669

Maybe I'm getting this wrong but I thought the providers package is for hooks/operators/sensor ?

That would go under airflow/providers/hashicorp/operator/

providers packages are for everything related to that specific provider