Fixed `mypy` code smells and added `mypy` to the CI/CD pipeline

[kushagra189]

Description

Ran mypy locally and removed the corresponding code smells detected. The current code is not compatible with mypy standards and checks for the same have been added to the CI/CD pipeline.

Fixes #140 and #141

Type of change

Please delete options that are not relevant.

• [ ] 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 not work as expected)
• [ ] Documentation update

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have updated the documentation (or documentation does not need to be updated)
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] I have not reduced the existing code coverage

[codecov[bot]]

Codecov Report

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

Coverage data is based on head (9cfb62d) compared to base (05be4df). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #143 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 19 19 Lines 953 966 +13 ========================================= + Hits 953 966 +13 ``` | [Impacted Files](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143?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/143/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% <ø> (ø)` | | | [foca/access\_control/access\_control\_server.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9hY2Nlc3NfY29udHJvbC9hY2Nlc3NfY29udHJvbF9zZXJ2ZXIucHk=) | `100.00% <100.00%> (ø)` | | | [foca/access\_control/foca\_casbin\_adapter/adapter.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9hY2Nlc3NfY29udHJvbC9mb2NhX2Nhc2Jpbl9hZGFwdGVyL2FkYXB0ZXIucHk=) | `100.00% <100.00%> (ø)` | | | [foca/access\_control/register\_access\_control.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9hY2Nlc3NfY29udHJvbC9yZWdpc3Rlcl9hY2Nlc3NfY29udHJvbC5weQ==) | `100.00% <100.00%> (ø)` | | | [foca/api/register\_openapi.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9hcGkvcmVnaXN0ZXJfb3BlbmFwaS5weQ==) | `100.00% <100.00%> (ø)` | | | [foca/config/config\_parser.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9jb25maWcvY29uZmlnX3BhcnNlci5weQ==) | `100.00% <100.00%> (ø)` | | | [foca/errors/exceptions.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9lcnJvcnMvZXhjZXB0aW9ucy5weQ==) | `100.00% <100.00%> (ø)` | | | [foca/factories/celery\_app.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9mYWN0b3JpZXMvY2VsZXJ5X2FwcC5weQ==) | `100.00% <100.00%> (ø)` | | | [foca/security/auth.py](https://codecov.io/gh/elixir-cloud-aai/foca/pull/143/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=elixir-cloud-aai#diff-Zm9jYS9zZWN1cml0eS9hdXRoLnB5) | `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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