Add myself (Dennis Felsing) as contributor

Summary: As my initial commit

Test Plan: Does not apply

Reviewers: ksreenivasan

Reviewed By: ksreenivasan

Differential Revision: https://phabricator.dev.yugabyte.com/D14620

CONTRIBUTORS.md

@@ -144,3 +144,4 @@ This is a list of people who have contributed code to the [YugabyteDB](https://g
 * [rthallamko3](https://github.com/rthallamko3)
 * [SteveSong](https://github.com/SteveXiSong)
 * [lnguyen](https://github.com/lnguyen-yugabyte)
+* [def-](https://github.com/def-)