[AIRFLOW-7015] Detect Dockerhub repo/user when building on Dockerhub

[potiuk]

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Issue link: AIRFLOW-7015

Make sure to mark the boxes below before creating PR: [x]

• Description above provides context of the change
• Commit message/PR title starts with [AIRFLOW-NNNN]. AIRFLOW-NNNN = JIRA ID^*
• Unit tests coverage for changes (not needed for documentation changes)
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^* For document-only changes commit message can start with [AIRFLOW-XXXX].

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In case of backwards incompatible changes please leave a note in UPDATING.md.
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[potiuk]

Simpler and restoring building on dockerhub

[codecov-io]

Codecov Report

Merging #7673 into master will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7673      +/-   ##
==========================================
+ Coverage   86.82%   86.95%   +0.12%     
==========================================
  Files         897      900       +3     
  Lines       42869    43603     +734     
==========================================
+ Hits        37223    37913     +690     
- Misses       5646     5690      +44

Impacted Files	Coverage Δ
...irflow/providers/google/cloud/hooks/datacatalog.py	91.74% <0%> (ø)
...ow/providers/google/cloud/operators/datacatalog.py	93.41% <0%> (ø)
...s/google/cloud/example_dags/example_datacatalog.py	100% <0%> (ø)
airflow/__init__.py	100% <0%> (+8%)	⬆️

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