Add reduced capacity note to issue template

[hsubox76]

Adding a note about reduced capacity during the holiday. Also adding some line breaks makes the commented-out text format better in the Github editor.

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Latest commit: 134a9a2

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[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (2333172) and head commit (acd5ef7).

Test Logs

• Base (23331723): https://github.com/firebase/firebase-js-sdk/actions/runs/428585912
• Head (acd5ef7c): https://github.com/firebase/firebase-js-sdk/actions/runs/429274822