test(cat-gateway): Signed doc test

[bkioshn]

Description

Implement signed document test in python

Related Issue(s)

Closes #1786

Description of Changes

• Change DB_URL in docker files to EVENT_DB_URL
• Add .py test where it correspond to signed_document.hurl
• Fix POST response in signed_document.hurl
• Fix path health check in api_tests

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 467/467}$ | ${\color{red}Fail: 0/467}$ |

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 467/467}$ | ${\color{red}Fail: 0/467}$ |

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 467/467}$ | ${\color{red}Fail: 0/467}$ |

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 476/481}$ | ${\color{red}Fail: 0/481}$ |

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 476/481}$ | ${\color{red}Fail: 0/481}$ |