feat(pg_dump): Add '--if-exists' option for pg_dump

[DmytroLitvinov]

Description

Add option --if-exists for pg_dump command.
Resolves #478

Checklist

Please update this checklist as you complete each item:

• Tests have been developed for bug fixes or new functionality.
• The changelog has been updated, if necessary.
• Documentation has been updated, if necessary.
• GitHub Issues closed by this PR have been linked.

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[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 91.03%. Comparing base (8f1307e) to head (d698c78).

❗ Current head d698c78 differs from pull request most recent head 5d27e34. Consider uploading reports for the commit 5d27e34 to get more accurate results

Files	Patch %	Lines
dbbackup/db/postgresql.py	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #511      +/-   ##
==========================================
- Coverage   91.40%   91.03%   -0.38%     
==========================================
  Files          19       19              
  Lines         873      859      -14     
  Branches      157      151       -6     
==========================================
- Hits          798      782      -16     
- Misses         40       41       +1     
- Partials       35       36       +1     

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[Archmonger]

I'm a bit uninformed here, but do you believe if exists should be the default behavior?

Also this can be merged after you create a simple unit test.

[DmytroLitvinov]

Hey @Archmonger ,
It is not activated by default: https://github.com/jazzband/django-dbbackup/pull/511/files#diff-c9b41b9008c36f1e459cfb74e2a4c827a8635d9aa1703a90ba0945439af62026R103 (we do not break existing code). So if someone needs it, they will provide that option.

[Archmonger]

Okay, I'm going to assume that you're saying having if_exists defaulting to False is the best choice.

[Archmonger]

This PR can be merged after you create a simple unit test.

[Archmonger]

Tests are broken, will need to be fixed.

[WillNilges]

Should be fixed in my branch. Sorry about that.

[Archmonger]

@DmytroLitvinov Can you remerge with his branch?

[DmytroLitvinov]

@Archmonger , could you help with the issue in CI?
https://github.com/jazzband/django-dbbackup/actions/runs/8678806552/job/23796332662?pr=511
Can't get what is going on here

[Archmonger]

Seems to be related the Python v3.7 tests

py37-django32: FAIL code 1 (19.58=setup[17.04]+cmd[2.54] seconds)

[Archmonger]

Marking this as draft due to tests failing