feat(StartThreadOptions): default autoArchiveDuration to channel's defaultAutoArchiveDuration

[ImRodry]

Please describe the changes this PR makes and why it should be merged:
This PR marks a thread's autoArchiveDuration parameter as optional when creating one, and defaults it to the channel's defaultAutoArchiveDuration when present. Otherwise, the Discord API will default it to 24 hours as seen in the upstream PR linked below

🌊 Upstream PR:

• Mark auto_archive_duration as optional when creating a thread discord/discord-api-docs#3567

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

[kyranet]

LGTM, waiting for upstream PR to be landed first.

[ImRodry]

Made this.channel.defaultArchiveDuration the default for autoArchiveDuration due to the conversation on the upstream PR where we found that Discord always defaults to 24h no matter what this is set to and passing null is ignored so it will replicate the default behavior of the API

[iCrawl]

I'm honestly not sure what to do with this PR in its current state and what seems to me like a Discord API bug.

[ImRodry]

I'm honestly not sure what to do with this PR in its current state and what seems to me like a Discord API bug.

I think we should wait to see what the dapi maintainers say about the other PR and if the bug gets fixed. If it does I can revert the last commit

[ImRodry]

Upstream PR has been merged