MudDataGrid: Add AggregateTemplate render fragment

[Anu6is]

Description

Currently when using column aggregates, users are restricted to outputting String values. This changes adds a new AggregateTemplate render fragment similar to the GroupTemplate render fragment that's available for grouping. Using the AggregateTemplate instead of the FooterTemplate as previously demonstrated in the Docs, gives the user access to the aggregated items instead of all page items.

Resolves #10410

How Has This Been Tested?

Visually

Type of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (fix or improvement to the website or code docs)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.51%. Comparing base (686f96c) to head (68cb099).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #10419   +/-   ##
=======================================
  Coverage   91.50%   91.51%           
=======================================
  Files         418      418           
  Lines       13225    13225           
  Branches     2538     2538           
=======================================
+ Hits        12102    12103    +1     
  Misses        549      549           
+ Partials      574      573    -1     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ScarletKuro]

LGTM, the solution is elegant.