docs: example of generated nonce to use base64 encoding as per spec

[csi-lk]

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.

[csi-lk]

CC @leerob who just wrote the documentation in this PR: #54601

[orca-security-us]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Secrets	0   1   0   0	View in Orca