Add upgrade notes

[nscuro]

Description

Adds upgrade notes.

While we do label breaking changes in pull requests and issues, we can't expect users to sift through all of them to determine whether any action is needed upon upgrading to a newer version.

This adds a new Upgrading page to the documentation, which will list notable and breaking changes for each version.

Addressed Issue

N/A

Additional Details

N/A

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have updated the migration changelog accordingly
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +2.67% (target: -1.00%)	✅ ∅ (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (9e2ead4)	172	140	81.40%
Head commit (fc38987)	6864 (+6692)	5770 (+5630)	84.06% (+2.67%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#1490)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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_{Codacy stopped sending the deprecated coverage status on June 5th, 2024. Learn more}