Capture cog load times using sentry performance tracking

[ChrisLovering]

I ran this once locally to make sure it all worked, and it looks great https://python-discord.sentry.io/performance/?project=2724195&statsPeriod=14d

[wookie184]

Nice, I'd thought about using this for commands, but figured it would be too noisy given some commands wait for user responses etc.

This seems good though.

[wookie184]

Looks good

[sentry]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ **ExtensionFailed: Extension 'bot.exts.info.python_news' raised an error: ResponseCodeError: Status: 500 Response: ** bot.exts.info.python_news View Issue
• ‼️ ExtensionFailed: Extension 'bot.exts.backend.sync' raised an error: ServerDisconnectedError: Server disconnected bot.exts.backend.sync View Issue
• ‼️ ExtensionFailed: Extension 'bot.exts.moderation.infraction.superstarify' raised an error: ResponseCodeError: Statu... bot.bot in load_extension View Issue

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