feat: add entry point for returning Celery app

[uniqueg]

Description

• provide method .create_celery_app() for class Foca that returns a configured Celery app
• can be used to avoid issues like circular imports that are likely to arise from the previous implementation
• bumps version to 0.11.0

Fixes #159

[codecov[bot]]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage :thumbsup:

Coverage data is based on head (dd20da9) compared to base (1223c64). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #160 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 20 20 Lines 967 974 +7 ========================================= + Hits 967 974 +7 ``` | [Impacted Files](https://codecov.io/gh/elixir-cloud-aai/foca/pull/160?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai) | Coverage Δ | | |---|---|---| | [foca/foca.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/160/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9mb2NhLnB5) | `100.00% <100.00%> (ø)` | | | [foca/version.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/160/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS92ZXJzaW9uLnB5) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai)

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