Add memory-usage to index and catalog telemetry reports

[patszt]

As suggested by @tobim it would be beneficial to have some memory usage being reported in the telemetry.
The measurement is not precise but it can still help when looking for a memory leak

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on vast.io, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

[tobim]

Almost good to go, just a few types need a real memusage instead of a bare sizeof.

[tobim]

This also needs an update to web/docs/setup-vast/monitor.md.

[tobim]

Code wise this looks good to me.