Add configuration parameters support for postgresql_database resource

[jBouyoud]

Description

This PR adds support for database-level configuration parameters to the postgresql_database resource, similar to what was implemented for roles in commit f625d09.

Changes

Core Implementation (resource_postgresql_database.go)

• Added parameter block to database schema with name, value, and quote attributes
• Implemented readDatabaseParameters() to read parameters from pg_database.datconfig
• Implemented setDatabaseConfigurationParameters() to apply changes via ALTER DATABASE SET/RESET
• Updated resourcePostgreSQLDatabaseReadImpl() to read parameters
• Updated resourcePostgreSQLDatabaseUpdate() to set parameters

Tests (resource_postgresql_database_test.go)

• Added TestAccPostgresqlDatabase_Parameters test covering:
  • Database creation with multiple parameters
  • Parameter updates and deletions
• Added testAccCheckDatabaseParameter() helper function

Documentation

• Updated website/docs/r/postgresql_database.html.markdown with:
  • Usage examples with parameter blocks
  • Complete documentation in "Argument Reference" section
• Added examples/database-with-parameters/ with practical examples

Usage Example

resource "postgresql_database" "my_db" {
  name = "my_db"

  parameter {
    name  = "work_mem"
    value = "16MB"
    quote = false
  }

  parameter {
    name  = "max_parallel_workers"
    value = "4"
    quote = false
  }
}

Generated SQL

Set parameter

ALTER DATABASE my_db SET work_mem TO 16MB;

Reset parameter

ALTER DATABASE my_db RESET work_mem;

Compatibility

• Compatible with all PostgreSQL versions supported by the provider
• Database-level configuration parameters are available since PostgreSQL 9.0+