docs: add 0.20.2 and 0.20.3 release notes to master

[ziggie1984]

Change

Master carries release notes for 0.20.0 and 0.20.1, and the 0.21 line is
complete through 0.21.2, but the 0.20 patch notes stopped being forward-ported
after 0.20.1:

release-notes-0.20.0.md
release-notes-0.20.1.md      <- 0.20.2 and 0.20.3 missing
release-notes-0.21.0.md
release-notes-0.21.1.md
release-notes-0.21.2.md
release-notes-0.22.0.md

This copies release-notes-0.20.2.md and release-notes-0.20.3.md over from
v0.20.x-branch so master holds the full historical record. Docs only — no code
changes, and nothing on the 0.21/0.22 notes is touched.

Provenance

Both files are copied verbatim from v0.20.x-branch (at f3d0f0035, after
#11045 landed). Verified by blob hash:

File	Blob	Matches
release-notes-0.20.2.md	f7463c95f	v0.20.x-branch and the published v0.20.2-beta tag
release-notes-0.20.3.md	82ed80798	v0.20.x-branch

The 0.20.3 file is the one created in #11045, which moved the entries that had
been appended to the already-published 0.20.2 notes after the v0.20.2-beta tag
into a notes file for the next patch release.

[saubyk]

Ack

[github-actions]

🟢 PR Severity: LOW

gh pr view | 2 files | 201 lines changed

🟢 Low (2 files)

• docs/release-notes/release-notes-0.20.2.md - release notes, docs-only change
• docs/release-notes/release-notes-0.20.3.md - release notes, docs-only change

Analysis

This PR only adds two release notes files under docs/release-notes/. No source code, wire protocol, wallet, channel, or database logic is touched, and the change is well below the file-count/line-count thresholds that would trigger a severity bump. Classified as LOW — best-effort review is sufficient.

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