docs: added info about new status codes

[frolvanya]

This PR is adding an information about new possible status codes that can be returned by jsonrpc

From now on, jsonrpc will start returning other HTTP codes than 200 OK for some errors:

• On internal server error it will return 500
• On timeout error it will return 408
• On request validation error will return 400

Changes were introduced in near/nearcore#11806 and near/nearcore#11822

[frolvanya]

@race-of-sloths please, include my PR in the Race

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Current status: executed

Reviewer	Score
@khorolets	1

Your contribution is much appreciated with a final score of 1!
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[khorolets]

Looks good to me! I realize it might be a bit uncomfortable to scroll the table horizontally, but all the information is here and consumable. Designing the docs is a different sort of task.

@race-of-sloths score 1

[telezhnaya]

Agree with the point that designing the doc is a separate job

LGTM