[FIX] web/database manager: fix MemoryError when restoring big databases

[olilau]

Description of the issue/feature this PR addresses:
When using the database manager to restore a very big zip with filestore
archive, a MemoryError can be raised by Python in the 'binascii' module
when Odoo web client is trying to convert the uploaded file to base6

Current behavior before PR:
Database restoration fails.

Desired behavior after PR is merged:
Database restoration succeeds.

I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

When using the database manager to restore a very big zip with filestore
archive, a MemoryError can be raised by Python in the 'binascii' module
when Odoo web client is trying to convert the uploaded file to base64.

This fix creates the base64 encoded data in chunks to avoid this issue.

The same fix is also used in the 'db' service when it received the base
64 encoded data and tries to convert it back to a file.

Closes issue 680195

[xmo-odoo]

Maybe using base64 streamreader/streamwriter could work with less additional complexity? E.g.

out = cStringIO()
shutil.copyfileobj(backup_file, codecs.getwriter('base64')(out))
data = out.getvalue()

and

reader = codecs.getreader('base64')(cStringIO(data))
shutil.copyfileobj(reader, data_file)

?

[antonylesuisse]

Data will still be O(dbsize) the solution would be to use an other api than

         request.session.proxy("db").restore(master_pwd, name, data, copy)

One that accept a fileobject.

[CGenie]

Please take a look at #21614

[C3POdoo]

Dear @olilau,

Thank you for your contribution but the version 9.0 is no longer supported.
We only support the last 3 stable versions so no longer accepts patches into this branch.

We apology if we could not look at your request in time.
If the contribution still makes sense for the upper version, please let us know and do not hesitate to recreate one for the recent versions. We will try to check it as soon as possible.

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