Merge pull request #308 from ipfs/release-v1.21.0-bis

Release v1.21.0

feat: v1.20 with check.ipfs.network button (#301)

* fix: add diagnostic-service-url flag

adds RAINBOW_DIAGNOSTIC_SERVICE_URL configuration option to expose
boxo/gateway's DiagnosticServiceURL setting. when gateway returns 504
timeout, users will see "Inspect retrievability of CID" button linking
to diagnostic service with CID as query parameter.

defaults to https://check.ipfs.network, can be disabled by setting to
empty string.

related to ipshipyard/roadmaps#14

* docs: clarify diagnostic service provider and self-hosting option

* chore: release v1.20.0

chore: release v1.19.0 (#299)

Merge pull request #291 from ipfs/release-v1.18.0

release v1.18.0

upgrade to boxo v0.33.1 (#282)

Merge pull request #274 from ipfs/release-v1.15.0

Release v1.15.0

Merge pull request #267 from ipfs/release-v1.14.0

Release v1.14.0

Merge pull request #263 from ipfs/release-v1.13.0

Release v1.13.0

Merge pull request #250 from ipfs/release-v1.12.0

Release v1.12.0

Release v1.11.0 (#249)

- tidy changelog
- update version