PG-2434 - Add Docker upgrade topic

[Andriciuc]

This PR mentions the docker upgrade image and instructs the user how to upgrade using this image. Furthermore, major upgrade chapter and docker install chapter will have links to this topic.

[mohitj1988]

Hi @Andriciuc - I am pasting detailed steps for doing a Major upgrade from PG 17 -> PG 18. You can use this to add more details to the documentation page.

Step 1: Create fresh directories for the old and new PostgreSQL clusters
mkdir -p ~/pgupgrade/pg17olddata/postgres
mkdir -p ~/pgupgrade/pg18newdata/postgres

Step 2: Start a PostgreSQL 17 container
docker run -d
--name pg17
-e POSTGRES_PASSWORD=password
-v ~/pgupgrade/pg17olddata/postgres:/data/db
percona/percona-distribution-postgresql:17

Step 3: Wait until PostgreSQL finishes initialization
docker logs pg17

Step 4: Connect to PostgreSQL
docker exec -it pg17 psql -U postgres

Step 5: Create a test database and some data
postgres=# CREATE DATABASE testdb;
postgres=# \c testdb
postgres=# CREATE TABLE t1(a int);
postgres=# INSERT INTO t1 VALUES (100);

Step 6: Stop the PostgreSQL 17 container
docker stop pg17

Step 7: Pull the upgrade image
docker pull percona/percona-distribution-postgresql-upgrade:18.4-17.10-16.14-15.18-14.23-1

Step 8: Run the upgrade
docker run --rm
--name ppg_upgrade_17_18
-e OLD_VERSION=17
-e NEW_VERSION=18
-e OLD_DATABASE_NAME=postgres
-e NEW_DATABASE_NAME=postgres
-v ~/pgupgrade/pg17olddata:/pgolddata
-v ~/pgupgrade/pg18newdata:/pgnewdata
percona/percona-distribution-postgresql-upgrade:18.4-17.10-16.14-15.18-14.23-1

Step 9: Start PostgreSQL 18 using the upgraded data directory
docker run -d
--name pg18
-e POSTGRES_PASSWORD=password
-v ~/pgupgrade/pg18newdata/postgres:/data/db
percona/percona-distribution-postgresql:18

Step 10: Verify PostgreSQL 18 starts successfully
docker logs -f pg18

Step 11: Connect to the upgraded cluster
docker exec -it pg18 psql -U postgres testdb

Step 12: Verify the upgraded data
postgres=# SELECT version();
postgres=# SELECT * FROM t1;