Added list_select_related to reduce duplicate SQL queries in admin UI

[phith0n]

Description of the Change

Added list_select_related in the admin IDTokenAdmin to avoid duplicate SQL queries.

Before adding the list_select_related, every 100 IDTokens 206 SQL queries is executed:

After adding the list_select_related, every 100 IDTokens 6 SQL queries is executed:

The total page loading time is 7305 milliseconds and 698 milliseconds respectively in my computer. It expects to reduce 10x the time.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #1177 (5e8963f) into master (007a5c4) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #1177 +/- ## ======================================= Coverage 96.85% 96.85% ======================================= Files 31 31 Lines 1812 1813 +1 ======================================= + Hits 1755 1756 +1  Misses 57 57 

Impacted Files	Coverage Δ
oauth2_provider/admin.py	100.00% <100.00%> (ø)

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[n2ygk]

Thanks for this!