Update award-index_statistics.sparql to make the graphic more straightforward

[Adafede]

Description

When looking at the current https://scholia.toolforge.org/award/#statistics, the first impression is that gender balance is "not so bad" as it seems there are quite some points above a "1/1 line", but this is heavily biased because the x and y axis do not share the same maximum.
This PR aims at fixing this.

Caveats

Currently, the manual max value has been set to 2,000.

Please list anything which has been left out of this PR or which should be considered before this PR is accepted
Check any of the following which apply:

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
  • I have made corresponding changes to the documentation
• This change requires new dependencies (please list)

If you make changes to the Python code

• My code passes the tox check, I can receive warnings about tests, documentation or both

Testing

Please describe the tests that you ran to verify your changes. Provide instructions, so we can reproduce. Please also list any relevant details for your test configuration.

• Test A
• Test B

Checklist

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have not used code from external sources without attribution
• I have considered accessibility in my implementation
• There are no remaining debug statements (print, console.log, ...)

[Adafede]

See https://w.wiki/8TqV (proposal) for comparison with https://w.wiki/8TqY (current)

[Adafede]

Same strategy could be applied to some other graphics (e.g. https://scholia.toolforge.org/publisher/Q233358#citations-works, just landed on it randomly)

[fnielsen]

Cherry-picked 974b55a