feat: Standardize environment variables for database connection.

[EdwinBetanc0urt]

Add DB_ENGINE environment variable, and unify alls DB_* redundant environment variables.

Additional context
The previous method of configuring databases still works, to provide backward compatibility, but priority is given to this proposed approach. In the future (in a major version), the previous method should be removed.

fixes #4677

[nginxproxymanagerci]

CI Error:

/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
certbot-node: Pulling from nginxproxymanager/nginx-full
Digest: sha256:a3f685a6ec6c4a3781242888fbfa53127abec9321d7ae871486ed2246693cdc4
Status: Image is up to date for nginxproxymanager/nginx-full:certbot-node
docker.io/nginxproxymanager/nginx-full:certbot-node
�[1;34m❯ �[1;36mTesting backend ...�[0m
yarn install v1.22.22
[1/4] Resolving packages...
[2/4] Fetching packages...
warning lru.min@1.1.2: The engine "bun" appears to be invalid.
warning lru.min@1.1.2: The engine "deno" appears to be invalid.
[3/4] Linking dependencies...
warning " > @apidevtools/swagger-parser@10.1.1" has unmet peer dependency "openapi-types@>=7".
[4/4] Building fresh packages...
Done in 8.56s.
yarn run v1.22.22
$ biome lint .
lib/config.js:67:33 lint/correctness/noInvalidUseBeforeDeclaration ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  × This variable is used before its declaration.
  
    65 │ 	if (envDataBaseEngne) {
    66 │ 		if (envDataBaseEngne === 'sqlite') {
  > 67 │ 			logger.info(`Using Sqlite: ${envSqliteFile}`);
       │ 			                             ^^^^^^^^^^^^^
    68 │ 			const defaultConection = dataBaseEngines[envDataBaseEngne];
    69 │ 			const envSqliteFile    = process.env.DB_SQLITE_FILE || '/data/database.sqlite';
  
  i The variable is declared here:
  
    67 │ 			logger.info(`Using Sqlite: ${envSqliteFile}`);
    68 │ 			const defaultConection = dataBaseEngines[envDataBaseEngne];
  > 69 │ 			const envSqliteFile    = process.env.DB_SQLITE_FILE || '/data/database.sqlite';
       │ 			      ^^^^^^^^^^^^^
    70 │ 			instance               = {
    71 │ 				database: {
  

Checked 83 files in 38ms. No fixes applied.
Found 1 error.
lint ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  × Some errors were emitted while running checks.
  

info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
error Command failed with exit code 1.