feat: Implemented Nagios Provider (#3960)

[deekshatomer]

/claim #3960
Closes #3960

Summary

Implemented the Nagios Provider for Keep.

Description:
-Added a new class NagiosProvider to integrate with Nagios.
-Implemented the fetch_alerts method to retrieve alerts from Nagios using HTTP requests.
-Created a unit test file (test_nagios_provider.py) to verify the functionality of the NagiosProvider class.
-Used unittest.mock to mock the fetch_alerts method in the test to avoid real HTTP requests.
-Verified that the test passes successfully.

Testing:
Ran the test file test_nagios_provider.py using pytest, and it passed without any issues.
Confirmed that the implementation works as expected with mocked responses.
/claim #3960

[vercel]

@deekshatomer is attempting to deploy a commit to the KeepHQ Team on Vercel.

A member of the Team first needs to authorize it.

[CLAassistant]

All committers have signed the CLA.

[deekshatomer]

hi ! @Matvey-Kuk Could you please review this PR? Thanks!

[Matvey-Kuk]

I see only tests in the proposed changes, not the provider itself 😢

[deekshatomer]

@Matvey-Kuk I have added the missing NagiosProvider class. Please review.

[Matvey-Kuk]

@deekshatomer I see you wrote a fetch_alerts method, but it's not following the design principles for providers. Also I see that the the documentation is missing. Will close the PR for now, please check other providers and feel free to open the PR one more time once it's ready.