slack credentials may fail when token rotation turned on

[riascho]

This PR adds information on why slack credentials may fail if the token rotation feature was turned on in the slack app.
I made a snippet so it can be used in two places: the slack credentials page and the slack trigger node page, as these are the most common places that users might look for help.

Please feel free to rephrase my wordings :) Thanks for the review!

[netlify]

✅ Deploy Preview for n8n-docs ready!

Name	Link
🔨 Latest commit	0b70ebe
🔍 Latest deploy log	https://app.netlify.com/sites/n8n-docs/deploys/674f2879d004a50008c587bb
😎 Deploy Preview	https://deploy-preview-2673--n8n-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[github-actions]

Overall readability score: 44.54 (🟢 +0.01)

File	Readability
token-rotation.md	64.31 (-)
slack.md	76.88 (🔴 -1.52)
n8n-nodes-base.slacktrigger.md	67.51 (🔴 -1.35)

View detailed metrics

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

File	Readability	FRE	GF	ARI	CLI	DCRS
token-rotation.md	64.31	61.36	10.59	11.2	10.1	7.42
	-	-	-	-	-	-
slack.md	76.88	60.61	6.23	9.4	10.94	6.24
	🔴 -1.52	🟢 +0	🔴 -0.05	🔴 -0.5	🔴 -0.46	🔴 -0.02
n8n-nodes-base.slacktrigger.md	67.51	56.45	8.52	11.1	11.24	6.82
	🔴 -1.35	🟢 +0	🔴 -0.04	🔴 -0.4	🔴 -0.34	🔴 -0.07

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	44.54	35.45	11.39	14.64	14.25	8.43
	🟢 +0.01	🟢 +0.02	🟢 +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

[imchairmanm]

Thanks @riascho! I pushed some small changes to try to make vale be quiet, but looks good otherwise. Thanks again!