Add Stratum-Session-Timeout

[ben221199]

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• You have checked the registry and found no current value that meets your needs.
• Your specification reference URL is stable; ideally, managed by a widely-recognised standards development organisation (e.g., published as an RFC). Otherwise, please give additional information below.

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• Field name: Stratum-Session-Timeout
• Status: permanent
• Specification document(s): https://github.com/bitcoin/bips/blob/master/bip-0040.mediawiki (when BIP40: Stratum wire protocol bitcoin/bips#1557 is merged)
• Comments:

Any additional information (this will not be included in the registry)?
URLs of BIPs are stable when merged. The specification is currently in the draft state.