db: switch driver to pgx5

[mastercactapus]

Description:
Updates the rest of the application to use pgx v5 from v4.

Out of Scope:
Migrating from github.com/jackc/pgtype -> github.com/jackc/pgx/v5/pgtype will be done in a separate PR.

Technical Details:
During the migration, we encountered the question of whether to use pgxpool.Pool or continue using sql.DB in a few places. Here are some insights into why certain choices were made:

• pgxpool.Pool is a native PGX type, while sql.DB is from the Go standard library.
• The swomsg package was previously using sql.DB and converting it into a pgx connection and back again, adding unnecessary boilerplate. This has been streamlined by directly using pgxpool.Pool.
• The pgxpool was used directly where possible elsewhere in the swo code to eliminate boilerplate code.
• The old AcquireConn method, which allowed fetching a PGX-native connection object from a sql.DB, has been removed in pgx v5, further justifying the use of pgxpool.Pool where possible.

The GoAlert application code continues to use Go's standard library interfaces (sql.DB), while the swo components have been upgraded to use the native PGX interfaces (pgxpool.Pool).