Add end-of-service note to line notify node and credential

[imchairmanm]

Adding a deprecation note on the Line node and credential since the service is shutting down next year.

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[github-actions]

Overall readability score: 44.18 (🟢 +0)

File	Readability
n8n-nodes-base.line.md	6.68 (🟢 +3.6)
line.md	66.08 (🔴 -2.52)

View detailed metrics

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

File	Readability	FRE	GF	ARI	CLI	DCRS
n8n-nodes-base.line.md	6.68	10.57	19	22	17.71	10.03
	🟢 +3.6	🔴 -0.51	🟢 +0	🟢 +0	🟢 +1.29	🟢 +0.58
line.md	66.08	43.29	7.62	11.1	12.74	6.41
	🔴 -2.52	🔴 -1.12	🔴 -0.47	🔴 -0.7	🔴 -0.41	🟢 +0.02

Averages:

	Readability	FRE	GF	ARI	CLI	DCRS
Average	44.18	35.22	11.44	14.7	14.29	8.46
	🟢 +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