fix: cpu contention on jwk reads + suppress duplicate jwk generation

[terev]

Using the reproduction steps included in #3863 I'm able to confirm this fixes the read contention:

bombardier -d 30s -t 30s -a -c 270 -l http://localhost:4444/.well-known/openid-configuration
Bombarding http://localhost:4444/.well-known/openid-configuration for 30s using 270 connection(s)
[==============================================================================================================================================================] 30s
Done!
Statistics        Avg      Stdev        Max
  Reqs/sec      3768.36    2589.36   12964.59
  Latency       71.76ms    29.92ms   579.56ms
  Latency Distribution
     50%    67.30ms
     75%    82.45ms
     90%    98.98ms
     95%   113.15ms
     99%   184.51ms
  HTTP codes:
    1xx - 0, 2xx - 112946, 3xx - 0, 4xx - 0, 5xx - 0
    others - 0
  Throughput:     7.70MB/s

I also noticed the .well-known/jwks.json route generates extra keys (if hammered before initialized) so I changed that handler to utilize the same duplicate suppression code.

Related issue(s)

Closes #3863

Checklist

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Further Comments

[aeneasr]

Great job everyone, thanks!

[terev]

🎉 Thanks for the well written initial report @awill1988 !

[awill1988]

Awesome fix @terev!