[feat] Implementing new release process (#200)

Streamlining the release process for mattermost-plugins by integrating release and signing pipelines under the delivery platform.

This update automates signing and releasing by simply pushing a semver tag(e.g: v0.0.1) or by using the newly introduced Makefile targets.
```
make patch
make minor
make major
```

For Release Candidades(RC):
```
make patch-rc
make minor-rc
make major-rc
```

Signed-off-by: Akis Maziotis <akis.maziotis@mattermost.com>

.github/workflows/cd.yml

@@ -1,18 +0,0 @@
-name: cd
-on:
-  workflow_run:
-    workflows: ["ci"]
-    branches-ignore: ["*"]
-    types:
-      - completed
-  push:
-    tags:
-      - "v*"
-
-permissions:
-  contents: read
-
-jobs:
-  plugin-cd:
-    uses: mattermost/actions-workflows/.github/workflows/plugin-cd.yml@main
-    secrets: inherit