fix: add missing bucket write permissions to downloader Lambda and cleanup IntHub references

[ceholden]

What I am changing

This PR,

• Fixes a missing PutObject and similar write permissions for the downloader Lambda. This was missing from our stack so I've added it manually in the meantime
• Removes references to IntHub from documentation and code, replacing it with mentions of "Copernicus Data Space Ecosystem" (CDSE) where relevant

It might be easier to review this PR commit-by-commit because there's relatively few lines of code changed for the actual bugfix versus for cleaning up SciHub/IntHub mentions

How I did it

• Add reference to the UPLOAD_BUCKET to our stack and add write permission to it for the downloader Lambda
• grep / delete or reword / repeat mentions of SciHub or IntHub

How you can test it

We can see the bucket permissions have been added via make diff from repo root (this runs cdk diff).

The USE_INTHUB toggle had been removed in previous work and has had no effect, so this change is a no-op other than some clean up.

[chuckwondo]

LGTM!