Add bazel-pipecd to gitignore (#3057)

**What this PR does / why we need it**:
Ignore bazel-pipecd because [changed the name of packages to pipecd](#3037).

**Which issue(s) this PR fixes**:

Fixes #

**Does this PR introduce a user-facing change?**:
<!--
If no, just write "NONE" in the release-note block below.
-->
```release-note
NONE
```

This PR was merged by Kapetanios.

Author: knanao

.gitignore

@@ -17,6 +17,7 @@
 /bazel-bin
 /bazel-genfiles
 /bazel-pipe
+/bazel-pipecd
 /bazel-out
 /bazel-testlogs
 /BUILD.bazel.generated