Update documentation for authenticated requests

[moisses89]

What it solves

Safe Decoder Service will be moved to the authenticate api gateway, so this PR updates the documentation accordingly.

[github-actions]

Branch preview

✅ Deployed successfully in branch deployment:

https://update__authenticated_decoder_api_doc--docs.review.5afe.dev

[github-actions]

Overall readability score: 35.96 (🟢 +0)

File	Readability
safe-decoder-service-reference.mdx	3.61 (🟢 +0)

View detailed metrics

🟢 - Shows an increase in readability
🔴 - Shows a decrease in readability

File	Readability	FRE	GF	ARI	CLI	DCRS
safe-decoder-service-reference.mdx	3.61	0	16.95	22	19	10.97
	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	35.96	31.85	13.17	16.51	15.19	8.71
	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0	🟢 +0

View metric targets

Metric	Range	Ideal score
Flesch Reading Ease	100 (very easy read) to 0 (extremely difficult read)	60
Gunning Fog	6 (very easy read) to 17 (extremely difficult read)	8 or less
Auto. Read. Index	6 (very easy read) to 14 (extremely difficult read)	8 or less
Coleman Liau Index	6 (very easy read) to 17 (extremely difficult read)	8 or less
Dale-Chall Readability	4.9 (very easy read) to 9.9 (extremely difficult read)	6.9 or less