This PR allows the Valkey users to perform conditional updates where the
SET command is completed if the given comparison-value matches the key’s
current value.
Syntax:
```
SET key value IFEQ comparison-value
```
Behavior:
If the values match, the SET completes as expected. If they do not
match, the command returns a (nil), except if the GET argument is also
given (see below).
Behavior with Additional Flags:
1. ```SET key value IFEQ comparison-value GET``` returns the existing
value, regardless of whether it matches comparison-value or not. The
conditional set operation is performed if the given comparison value
matches the existing value. To check if the SET succeeded, the caller
needs to check if the returned string matches the comparison-value.
2. ```SET key value IFEQ comparison-value XX``` is a syntax error.
3. ```SET key value IFEQ comparison-value NX``` is a syntax error.
Closes: #1215
---------
Signed-off-by: Sarthak Aggarwal <sarthagg@amazon.com>
9cfe1b3d81