feat: add new app event hooks for custom build scripts

[shazron]

The current event hooks are defined at https://www.adobe.io/apis/experienceplatform/project-firefly/docs.html#!AdobeDocs/project-firefly/master/guides/app-hooks.md

These are the current list of 6 hooks. Note that they do not apply to all commands, only some (for example, deploy hooks don't apply to aio app run):

1. pre-app-run
2. pre-app-build
3. post-app-build
4. pre-app-deploy
5. post-app-deploy
6. post-app-run

The new list would contain 4 new hooks, and would apply to all applicable commands:

1. pre-app-run
2. pre-app-build
3. build-actions (replaces default tooling if present)
4. build-static (replaces default tooling if present)
5. post-app-build
6. pre-app-deploy
7. deploy-actions (replaces default tooling if present)
8. deploy-static (replaces default tooling if present)
9. post-app-deploy
10. post-app-run

Motivation

There are some apps that need to customize:

1. how the static files are being built (custom webpack for example)
2. how the actions are being built (package all static files in a folder with the action without needing to specify as include in manifest.yml for example -- to include template files for serving up later)

[aiojbot]

JIRA issue created: https://jira.corp.adobe.com/browse/ACNA-976

[shazron]

PR #340