feat(metrics): add conversion webhook metrics

[nojnhuh]

Description:
This change adds the osm_conversion_webhook_resource_total metric to
count custom resource conversions between API versions.

Part of #4568

Example:

osm_conversion_webhook_resource_total{from_version="config.openservicemesh.io/v1alpha1",kind="MeshConfig",success="true",to_version="config.openservicemesh.io/v1alpha2"} 1

Testing done:

• Updated unit tests
• Did some manual smoke testing with the whole control plane running and creating/updating/deleting a v1alpha1 MeshConfig

Affected area:

Functional Area
New Functionality	[X]
CI System	[ ]
CLI Tool	[ ]
Certificate Management	[ ]
Control Plane	[ ]
Demo	[ ]
Documentation	[ ]
Egress	[ ]
Ingress	[ ]
Install	[ ]
Networking	[ ]
Observability	[X]
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)? Yes, add conversion webhook metric osm-docs#344

[codecov-commenter]

Codecov Report

Merging #4606 (0311eda) into main (aaa7f30) will increase coverage by 0.05%.
The diff coverage is 92.50%.

@@            Coverage Diff             @@
##             main    #4606      +/-   ##
==========================================
+ Coverage   69.14%   69.20%   +0.05%     
==========================================
  Files         216      216              
  Lines       15000    15028      +28     
==========================================
+ Hits        10372    10400      +28     
  Misses       4576     4576              
  Partials       52       52              

Flag	Coverage Δ
unittests	69.20% <92.50%> (+0.05%)	⬆️

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

Impacted Files	Coverage Δ
cmd/osm-bootstrap/osm-bootstrap.go	45.59% <0.00%> (-0.72%)	⬇️
pkg/crdconversion/crdconversion.go	75.53% <100.00%> (+0.72%)	⬆️
pkg/crdconversion/framework.go	74.56% <100.00%> (+6.88%)	⬆️
pkg/metricsstore/metricsstore.go	92.17% <100.00%> (+0.27%)	⬆️

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