Upgrade all extensions to node18

[dackers86]

Node16 end-of-life has been brought forward. Source: https://nodejs.org/en/blog/announcements/nodejs16-eol

• export-user-data (chore(export-user-data): upgrade to node18 #60)
• firestore-record-acknowledgments (chore(firestore-record-acknowledgments): upgrade to node18 #61)
• image-processing-api (chore(image-processing-api): upgrade to node18 #62)