Scope and purpose

Add a partial btree index on netboxentity.deviceid to speed up lookups by device. Without this index, Django-generated queries filtering netboxentity by deviceid result in sequential scans.

On a large production install, this reduced mean execution time of device-related entity lookups from 30265ms to 0.076ms (~400,000x improvement).

The schema change script drops any existing index by the same name before creating the standard one, to handle installations that may have already defined a local index.

Contributor Checklist

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
• Linted/formatted the code with ruff, easiest by using pre-commit
• Wrote the commit message so that the first line continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• Based this pull request on the correct upstream branch: For a patch/bugfix affecting the latest stable version, it should be based on that version's branch (<major>.<minor>.x). For a new feature or other additions, it should be based on master.
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If it's not obvious from a linked issue, described how to interact with NAV in order for a reviewer to observe the effects of this change first-hand (commands, URLs, UI interactions)
• If this results in changes in the UI: Added screenshots of the before and after
• If this adds a new Python source code file: Added the boilerplate header to that file