Add support for `XX` in `SET` command

[arpitbbhayani]

We already have the SET command implemented. Now we need to add support for XX option similar to the XX option in Redis. Please refer to the following commit in Redis to understand the implementation specifics - source.

Write unit and integration tests for the command referring to the tests written in the Redis codebase 7.2.5. For integration tests, you can refer to the tests folder. Note: they have used TCL for the test suite, and we need to port that to our way of writing integration tests using the relevant helper methods. Please refer to our tests directory.

For the command, benchmark the code and measure the time taken and memory allocs using benchmem and try to keep them to the bare minimum.

[sanuj96]

In am interested to work on it. Can you please assign this to me @arpitbbhayani ?