ref(cert): remove expiration field from osm-ca-bundle secret data

[jaellio]

Description:

Removes the use of the required expiration date data field in the
osm-ca-bundle. The certificate's expiration can be obtained
directly from the certificate rather than from the expiration
field.

This change also updates the logs in GetCertificateFromSecret to
reflect the broader use of the function.

Updates ca_test.go to use go testing package rather than ginko
and gomega. Adds checks for notAfter and expiration values on
the x509 certificate and the certificator respectively.

Note: It is no longer necessary to perform any formatting on
expiration time.

Resolves #4467

Testing done:

• Updated unit tests to verify the expiration is correctly set using the notAfter value obtained from the decoded x509 cert
• On a kind cluster ran the automated demo
  • verified osm-ca-bundle formatting when it was created by OSM using Tresor as the certificate provider
  • verified OSM successfully obtained data from the osm-ca-bundle secret without an expiration field when created by the user

Affected area:

Functional Area
New Functionality	[ ]
CI System	[ ]
CLI Tool	[ ]
Certificate Management	[x]
Control Plane	[ ]
Demo	[ ]
Documentation	[ ]
Egress	[ ]
Ingress	[ ]
Install	[ ]
Networking	[ ]
Observability	[ ]
Performance	[ ]
SMI Policy	[ ]
Security	[ ]
Sidecar Injection	[ ]
Tests	[ ]
Upgrade	[ ]
Other	[ ]

Please answer the following questions with yes/no.

1. Does this change contain code from or inspired by another project? No

   • Did you notify the maintainers and provide attribution?

2. Is this a breaking change? No

3. Has documentation corresponding to this change been updated in the osm-docs repo (if applicable)? No - will make a follow-up PR in the docs repo

[codecov-commenter]

Codecov Report

Merging #4472 (8674854) into main (a0c9a86) will decrease coverage by 0.04%.
The diff coverage is 53.84%.

@@            Coverage Diff             @@
##             main    #4472      +/-   ##
==========================================
- Coverage   69.19%   69.14%   -0.05%     
==========================================
  Files         212      212              
  Lines       14580    14573       -7     
==========================================
- Hits        10089    10077      -12     
- Misses       4439     4444       +5     
  Partials       52       52              

Flag	Coverage Δ
unittests	69.14% <53.84%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/certificate/providers/tresor/ca.go	68.96% <44.44%> (-3.19%)	⬇️
pkg/certificate/providers/config.go	76.76% <75.00%> (-1.37%)	⬇️

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[shashankram]

Thanks @jaellio