feat: use XORM EngineGroup instead of single Engine connection (#7212)

Resolves #7207

Add new configuration to make XORM work with a main and replicas database instances. The follow configuration parameters were added:

- `HOST_PRIMARY`
- `HOST_REPLICAS`
- `LOAD_BALANCE_POLICY`. Options:
    - `"WeightRandom"` -> `xorm.WeightRandomPolicy`
    - `"WeightRoundRobin`  -> `WeightRoundRobinPolicy`
    - `"LeastCon"` -> `LeastConnPolicy`
    - `"RoundRobin"` -> `xorm.RoundRobinPolicy()`
    - default: `xorm.RandomPolicy()`
- `LOAD_BALANCE_WEIGHTS`

Co-authored-by: pat-s <patrick.schratz@gmail.com@>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7212
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: pat-s <patrick.schratz@gmail.com>
Co-committed-by: pat-s <patrick.schratz@gmail.com>

modules/testlogger/testlogger.go

@@ -364,6 +364,9 @@ var ignoredErrorMessage = []string{
 	// TestDatabaseCollation
 	`[E] [Error SQL Query] INSERT INTO test_collation_tbl (txt) VALUES ('main') []`,
 
+	// Test_CmdForgejo_Actions
+	`DB: No dedicated replica host defined; falling back to primary DSN for replica connections`,
+
 	// TestDevtestErrorpages
 	`ErrorPage() [E] Example error: Example error`,
 }