fix: rename application factory

[afuetterer]

Description

This PR fixes a bug that was introduced in #421.

• rename application factory to follow flask conventions (create_fuji_app -> create_app)
• remove obsolete .parent resulting in wrong path in create_app

Related issue: #390

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Checklist

• I have read the contributor guide.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[github-actions]

📋 Pytest Results

19 tests  +19   18 ✔️ +18   27s ⏱️ +27s
  1 suites +  1     0 💤 ±  0 
  1 files   +  1     1 ❌ +  1 

For more details on these failures, see this check.

Results for commit 086002c. ± Comparison against base commit 8a306e5.

♻️ This comment has been updated with latest results.

[github-actions]

Package	Line Rate	Branch Rate	Health
.	50%	35%	❌
config	100%	100%	✔
controllers	86%	58%	✔
evaluators	66%	39%	➖
harvester	65%	55%	➖
helper	62%	52%	➖
models	81%	87%	✔
Summary	70% (6541 / 9326)	60% (2741 / 4541)	➖