chore: upgrade docker-compose & CI postgres version to 15

What are the relevant tickets?

Description (What does it do?)

This PR upgrades the docker-compose & CI PostgreSQL version to 15.

How can this be tested?

Check out this branch and follow one of the solutions below to upgrade the PostgreSQL version in your local environment (with or without data migration):

With Data Migration:

Follow these steps to upgrade PostgreSQL with data migration:

# 1. Using your old 12.19 database:
docker-compose exec -T db pg_dumpall -h db -U postgres > db_backup.sql
# 2. stop all containers
docker-compose stop
# 3 destroy the old database container
docker-compose rm -sv db
# 4. build+start the new database container
docker-compose up db -d
# 5. restore the database from backup
docker cp db_backup.sql $(docker-compose ps -q db):/tmp/backup.sql
docker-compose exec -T db psql -U postgres -d postgres -f /tmp/backup.sql
# 6. start the remaining containers
docker-compose up
# 7 verify postgres 15 is in use:
docker-compose exec -e PGPASSWORD=postgres db psql -h db -U postgres

Note: If you encounter password authentication failed for user "postgres" in STEP 6 due to no password being set for the user "postgres" in the SQL backup file, update the user password through the SQL shell docker-compose exec -it db psql -U postgres postgres:

ALTER USER postgres PASSWORD 'postgres';

Without Data Migration

Follow these steps to upgrade PostgreSQL without data migration:

docker-compose down
docker-compose up -d

Note: These commands will cleanly restart your Docker Compose setup.

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🔎 Detected hardcoded secret in your pull request

| GitGuardian id | GitGuardian status | Secret | Commit | Filename | | | -------------- | ------------------ | ------------------------------ | ---------------- | --------------- | -------------------- | | [9430286](https://dashboard.gitguardian.com/workspace/71358/incidents/9430286?occurrence=142913727) | Triggered | Generic Password | d0a35796c470afb3a2d21707aea7aafb94acc7a4 | docker-compose.yml | [View secret](https://github.com/mitodl/mitxpro/commit/d0a35796c470afb3a2d21707aea7aafb94acc7a4#diff-e45e45baeda1c1e73482975a664062aa56f20c03dd9d64a827aba57775bed0d3L28) |

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mitodl / mitxpro