reduce stack size requirement for this library by 4k my moving a buffer to heap. (espressif#6745)

Better allocate the buffer for f_mkfs from the heap otherwise the stack requirement of this library is huge due to a work buffer allocated for f_mkfs in sdcard_mount. The work buffer is only needed if argument format_if_empty is set true (which is by default false). 
This change is quite important if you plan to use this library in a task. as now it increased the tasks stacks size by 4k, even this memory is never used if users are not aware of the large stack requirement during init this library may have other variables on stack that would have written memory outsides its range which can cause various side effects.

Co-authored-by: Jan Procházka <90197375+P-R-O-C-H-Y@users.noreply.github.com>

Author: mazgch

libraries/SD/src/sd_diskio.cpp

@@ -801,8 +801,13 @@ bool sdcard_mount(uint8_t pdrv, const char* path, uint8_t max_files, bool format
     if (res != FR_OK) {
         log_e("f_mount failed: %s", fferr2str[res]);
         if(res == 13 && format_if_empty){
-            BYTE work[FF_MAX_SS];
+            BYTE* work = (BYTE*) malloc(sizeof(BYTE) * FF_MAX_SS);
+            if (!work) {
+              log_e("alloc for f_mkfs failed");
+              return false;
+            }
             res = f_mkfs(drv, FM_ANY, 0, work, sizeof(work));
+            free(work);
             if (res != FR_OK) {
                 log_e("f_mkfs failed: %s", fferr2str[res]);
                 esp_vfs_fat_unregister_path(path);