Update default graph for 'Publications by Academic Age Group'

[wwelling]

• Change Researchers scale on x-axis to maximum of 1000 with increments of 200. (e.g 0, 200, 400, 600, 800, 1000)
• Update color scheme, use Maroon for lines and grey for bars. (Reference TAMU style guide)
• Use theme variable as available.
• Here is how current graph looks like:

[C2H5-M]

Here's a sample gray chart with maroon lines.

[wwelling]

https://github.com/TAMULib/scholars-discovery/blob/tamu-main/src/main/resources/defaults/themes.yml#L292

[wwelling]

https://github.com/TAMULib/scholars-angular/blob/tamu-main/src/app/core/model/theme/theme.ts

[wwelling]

https://github.com/TAMULib/scholars-angular/blob/tamu-main/src/app/core/store/theme/index.ts#L38C14-L38C37

[wwelling]

https://github.com/TAMULib/scholars-angular/blob/tamu-main/src/app/%2Bdata-and-analytics/academic-age-group/barplot/barplot.component.ts