Add core config parameter to galexie config admin guide (#1799)

Author: chowbao

docs/data/indexers/build-your-own/galexie/admin_guide/configuring.mdx

@@ -52,3 +52,31 @@ ledgers_per_file = 1
 # Number of files per partition/directory
 files_per_partition = 64000
 ```
+
+##### Use a Custom Core Config (Optional)
+
+You can specify a custom `core.cfg` file in the Galexie `config.toml` to use that will override the default core parameters used with the Stellar Network specified in the `network` parameter.
+
+Copy an existing `core.cfg` file such as the `captive-core-pubnet.cfg` provided [here](https://github.com/stellar/go/blob/master/ingest/ledgerbackend/configs/captive-core-pubnet.cfg) and add the following to your `config.toml`
+
+```toml
+captive_core_toml_path = "my-captive-core.cfg"
+```
+
+- Please see the [Choosing Your Quorum Set](../../../../../validators/admin-guide/configuring.mdx#choosing-your-quorum-set) for more information about `core.cfg` quorum set configuration
+- A list of customizable core parameters can be found [here](https://github.com/stellar/stellar-core/blob/master/src/main/Config.h)
+
+The default `core.cfg` used by Galexie will enable the following core parameters:
+
+- **BACKFILL_RESTORE_META -** ledger metadata will be populated with LedgerEntryChange RESTORE type for protocol versions prior to 23
+- **ENABLE_SOROBAN_DIAGNOSTIC_EVENTS -** additional diagnostic Soroban events that are not part of the protocol will be generated while applying Soroban transactions
+- **EMIT_SOROBAN_TRANSACTION_META_EXT_V1 -** Soroban extension V1 data will be emitted
+- **EMIT_LEDGER_CLOSE_META_EXT_V1 -** ledger metadata extension V1 data will be emitted
+- **EMIT_CLASSIC_EVENTS -** classic events will be enabled and emitted for protocol `>= 23`
+- **BACKFILL_STELLAR_ASSET_EVENTS -** classic events will be enabled and emitted for protocol `<= 22`. This parameter also requires `EMIT_CLASSIC_EVENTS` to be enabled
+
+:::warning
+
+When you provide a custom core configuration file, it completely replaces the Galexie's default core configuration. This means you must explicitly set any parameters you want to enable, including the ones that are enabled by default in Galexie. Any parameter not listed in your custom config will be set to false.
+
+:::