docs: example of generated nonce to use base64 encoding as per spec (#55039)
nonce's are limited to characters found in base64 encoding, uuids contain '-' which breaks the spec,
converting to a base64 string after generating simplifies this
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This was a bit gotcha in our project, there are a few tools that only expect there to be a single `-` and do a split based off it (so when there are >1 they fail)
## Rules for nonce's
- The nonce must be unique for each HTTP response
- The nonce should be generated using a cryptographically secure random generator
- The nonce should have sufficient length, aim for at least 128 bits of entropy (32 hex characters, or about 24 base64 characters).
- Script tags that have a nonce attribute must not have any untrusted / unescaped variables within them.
- The characters that can be used in the nonce string are limited to the characters found in base64 encoding.