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>
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