certificate/vault: Change cache from a map to sync.Map

[draychev]

This PR removes the cacheLock mutex from Certificate{} and uses a sync.Map instead of *map[certificate.CommonName]certificate.Certificater

ref #507

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Affected area:

• New Functionality [ ]
• Documentation [ ]
• Install [ ]
• Control Plane [ ]
• CLI Tool [ ]
• Certificate Management [ ]
• Networking [ ]
• Metrics [ ]
• SMI Policy [ ]
• Security [ ]
• Tests [ ]
• CI System [ ]
• Performance [ ]
• Other [ ]

Please answer the following questions with yes/no.

• Does this change contain code from or inspired by another project? If so, did you notify the maintainers and provide attribution?

[codecov-io]

Codecov Report

Merging #2074 (b83626b) into main (aa9409e) will increase coverage by 0.05%.
The diff coverage is 45.45%.

@@            Coverage Diff             @@
##             main    #2074      +/-   ##
==========================================
+ Coverage   57.93%   57.99%   +0.05%     
==========================================
  Files         143      143              
  Lines        5851     5842       -9     
==========================================
- Hits         3390     3388       -2     
+ Misses       2458     2451       -7     
  Partials        3        3              

Impacted Files	Coverage Δ
pkg/certificate/providers/vault/types.go	100.00% <ø> (ø)
...certificate/providers/vault/certificate_manager.go	50.00% <25.00%> (+1.80%)	⬆️
pkg/certificate/providers/vault/debugger.go	100.00% <100.00%> (ø)
pkg/envoy/route/config.go	96.03% <0.00%> (+0.79%)	⬆️

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