Add RM_RdbLoad and RM_RdbSave module API functions (#11852)

Add `RM_RdbLoad()` and `RM_RdbSave()` to load/save RDB files from the module API. 

In our use case, we have our clustering implementation as a module. As part of this
implementation, the module needs to trigger RDB save operation at specific points.
Also, this module delivers RDB files to other nodes (not using Redis' replication).
When a node receives an RDB file, it should be able to load the RDB. Currently,
there is no module API to save/load RDB files. 


This PR adds four new APIs:
```c
RedisModuleRdbStream *RM_RdbStreamCreateFromFile(const char *filename);
void RM_RdbStreamFree(RedisModuleRdbStream *stream);

int RM_RdbLoad(RedisModuleCtx *ctx, RedisModuleRdbStream *stream, int flags);
int RM_RdbSave(RedisModuleCtx *ctx, RedisModuleRdbStream *stream, int flags);
```

The first step is to create a `RedisModuleRdbStream` object. This PR provides a function to
create RedisModuleRdbStream from the filename. (You can load/save RDB with the filename).
In the future, this API can be extended if needed: 
e.g., `RM_RdbStreamCreateFromFd()`, `RM_RdbStreamCreateFromSocket()` to save/load
RDB from an `fd` or a `socket`. 


Usage:
```c
/* Save RDB */
RedisModuleRdbStream *stream = RedisModule_RdbStreamCreateFromFile("example.rdb");
RedisModule_RdbSave(ctx, stream, 0);
RedisModule_RdbStreamFree(stream);

/* Load RDB */
RedisModuleRdbStream *stream = RedisModule_RdbStreamCreateFromFile("example.rdb");
RedisModule_RdbLoad(ctx, stream, 0);
RedisModule_RdbStreamFree(stream);
```

1 files changed, 1 insertions, 0 deletions

diff --git a/runtest-moduleapi b/runtest-moduleapi
index d5010edc1..ff685afb6 100755
--- a/runtest-moduleapi
+++ b/runtest-moduleapi
@@ -54,4 +54,5 @@ $TCLSH tests/test_helper.tcl \
 --single unit/moduleapi/postnotifications \
 --single unit/moduleapi/async_rm_call \
 --single unit/moduleapi/moduleauth \
+--single unit/moduleapi/rdbloadsave \
 "${@}"