Merge branch 'main' into archive-v21.2 and fix broken image references

- Fixed broken v21.2 storage layer image references by updating each version
  to use its own images (sst.png, lsm-with-ssts.png, memtable-wal-sst.png)
- Resolved merge conflicts by confirming deletion of v21.2 files
- Updated archived-documentation.md to include both v21.2 and v19.2

Author: ebembi-crdb

src/current/_includes/releases/v20.2/v20.2.13.md

@@ -22,8 +22,8 @@ Release Date: July 12, 2021
 
 <h3 id="v20-2-13-bug-fixes">Bug fixes</h3>
 
-- Fixed a bug which prevented the [optimizer](https://www.cockroachlabs.com/docs/v21.1/cost-based-optimizer) from producing plans with [partial indexes](https://www.cockroachlabs.com/docs/v21.1/partial-indexes) when executing some prepared statements that contained placeholders, stable functions, or casts. This bug was present since partial indexes were added in v20.2.0. [#66641][#66641]
-- Fixed a panic that could occur in the [optimizer](https://www.cockroachlabs.com/docs/v21.1/cost-based-optimizer) when executing a prepared plan with placeholders. This could happen when one of the tables used by the query had [computed columns](https://www.cockroachlabs.com/docs/v21.1/computed-columns) or a [partial index](https://www.cockroachlabs.com/docs/v21.1/partial-indexes). [#66832][#66832]
+- Fixed a bug which prevented the optimizer from producing plans with partial indexes when executing some prepared statements that contained placeholders, stable functions, or casts. This bug was present since partial indexes were added in v20.2.0. [#66641][#66641]
+- Fixed a panic that could occur in the optimizer when executing a prepared plan with placeholders. This could happen when one of the tables used by the query had computed columns or a partial index. [#66832][#66832]
 - Fixed a bug that caused graceful drain to call `time.sleep` multiple times, which cut into the time needed for range [lease transfers](https://www.cockroachlabs.com/docs/v20.2/architecture/replication-layer#leases). [#66852][#66852]
 - CockroachDB now allows a node with [lease](https://www.cockroachlabs.com/docs/v20.2/architecture/replication-layer#leases) preferences to drain gracefully. [#66714][#66714]
 - CockroachDB now avoids interacting with [decommissioned nodes](https://www.cockroachlabs.com/docs/v20.2/remove-nodes) during [DistSQL](https://www.cockroachlabs.com/docs/v20.2/architecture/sql-layer#distsql) planning and consistency checking. [#66951][#66951]