Make INFO command variadic (#6891)

This is an enhancement for INFO command, previously INFO only support one argument
for different info section , if user want to get more categories information, either perform
INFO all / default or calling INFO for multiple times.

**Description of the feature**

The goal of adding this feature is to let the user retrieve multiple categories via the INFO
command, and still avoid emitting the same section twice.

A use case for this is like Redis Sentinel, which periodically calling INFO command to refresh
info from monitored Master/Slaves, only Server and Replication part categories are used for
parsing information. If the INFO command can return just enough categories that client side
needs, it can save a lot of time for client side parsing it as well as network bandwidth.

**Implementation**
To share code between redis, sentinel, and other users of INFO (DEBUG and modules),
we have a new `genInfoSectionDict` function that returns a dict and some boolean flags
(e.g. `all`) to the caller (built from user input).
Sentinel is later purging unwanted sections from that, and then it is forwarded to the info `genRedisInfoString`.

**Usage Examples**
INFO Server Replication   
INFO CPU Memory
INFO default commandstats

Co-authored-by: Oran Agra <oran@redislabs.com>

tests/unit/moduleapi/infotest.tcl

@@ -64,7 +64,7 @@ start_server {tags {"modules"}} {
     }
 
     test {module info one module} {
-        set info [r info INFOTEST]
+        set info [r info INFOtest] ;# test case insensitive compare
         # info all does not contain modules
         assert { [string match "*Spanish*" $info] }
         assert { ![string match "*used_memory*" $info] }
@@ -72,7 +72,7 @@ start_server {tags {"modules"}} {
     } {-2}
 
     test {module info one section} {
-        set info [r info INFOTEST_SPANISH]
+        set info [r info INFOtest_SpanisH] ;# test case insensitive compare
         assert { ![string match "*used_memory*" $info] }
         assert { ![string match "*Italian*" $info] }
         assert { ![string match "*infotest_global*" $info] }
@@ -90,6 +90,31 @@ start_server {tags {"modules"}} {
         assert_match {*infotest_unsafe_field:value=1*} $info
     }
 
+    test {module info multiply sections without all, everything, default keywords} {
+        set info [r info replication INFOTEST]
+        assert { [string match "*Spanish*" $info] }
+        assert { ![string match "*used_memory*" $info] }
+        assert { [string match "*repl_offset*" $info] }
+    }
+
+    test {module info multiply sections with all keyword and modules} {
+        set info [r info all modules]
+        assert { [string match "*cluster*" $info] }
+        assert { [string match "*cmdstat_info*" $info] }
+        assert { [string match "*infotest_global*" $info] }
+    }
+
+    test {module info multiply sections with everything keyword} {
+        set info [r info replication everything cpu]
+        assert { [string match "*client_recent*" $info] }
+        assert { [string match "*cmdstat_info*" $info] }
+        assert { [string match "*Italian*" $info] }
+        # check that we didn't get the same info twice
+        assert { ![string match "*used_cpu_user_children*used_cpu_user_children*" $info] }
+        assert { ![string match "*Italian*Italian*" $info] }
+        field $info infotest_dos
+    } {2}
+
     test "Unload the module - infotest" {
         assert_equal {OK} [r module unload infotest]
     }