docs: document version support deprecation policy

[JuroUhlar]

• Document that Node SDK v7.x (Server API v4) is fully supported
• Note that previous major versions targeting Server API v3 are deprecated and only receive security fixes
• Nest the existing semantic versioning notes under the new section

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7f301f9

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[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟢	Statements	98.15%	159/162
🟢	Branches	96.84%	92/95
🟢	Functions	100%	35/35
🟢	Lines	98.11%	156/159

Test suite run success

83 tests passing in 24 suites.

Report generated by 🧪jest coverage report action from 7f301f9

Show full coverage report

St	File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
🟢	All files	98.14	96.84	100	98.11
🟢	src	98.43	98.66	100	98.41
🔴	...edApiTypes.ts	0	0	0	0
🔴	index.ts	0	0	0	0
🟢	sealedResults.ts	100	100	100	100
🟢	...rApiClient.ts	96.15	97.22	100	96.15	358,362
🟢	types.ts	100	100	100	100
🟢	urlUtils.ts	100	100	100	100
🟢	webhook.ts	100	100	100	100
🟢	src/errors	97.05	90	100	96.96
🟢	apiErrors.ts	100	100	100	100
🟢	...orResponse.ts	100	100	100	100
🟢	toError.ts	87.5	88.88	100	87.5	21
🟢	unsealError.ts	100	50	100	100	10

[github-actions]

⚠️ This PR doesn't contain any changesets. If there are user-facing changes, don't forget to run:

pnpm exec changeset

to create a changeset.