Add flag EDXAPP_REINDEX_ALL_COURSES (reindex courses on deploy)

Description

This adds a task to call reindex_course on deploy. Togglable through a flag `EDXAPP_REINDEX_ALL_COURSES` (disabled by default).

*JIRA tickets*: N/A

*Discussions*: N/A

*Dependencies*: None

*Screenshots*:

*Sandbox URL*: TBD - sandbox is being provisioned.

*Merge deadline*: None

*Testing instructions*:

1. Do a deploy with this variable set to False. Nothing should change
2. Temporarily add a tag to the new task („reindex all courses“) in deploy.yml: `testing-clemente-reindex-courses`. This will be used in the ansible-playbook invocation.
2. Test in local in an already deployed devstack with some course, with:
```bash
cd /edx/app/edx_ansible
source venvs/edx_ansible/bin/activate
cd edx_ansible/playbooks/
ansible-playbook -e "{role: 'edxapp'}" -i "localhost," -c local --tags testing-clemente-reindex-courses run_role.yml -e EDXAPP_REINDEX_ALL_COURSES=true -e edxapp_settings=devstack -vvv
```
7. Verify (in the verbose info) that some courses are processed and reindexed

*Author notes and concerns*:

  • This is supposed to be a one-time operation, on deploy, for the cases when an instance is using a local ElasticSearch.

  • The command doesn't depend on any particular ModuleStore

*Reviewers*

  • [x] @pomegranited

  • [ ] edX reviewer[s] TBD

*Settings*
```yaml
EDXAPP_REINDEX_ALL_COURSES: true
```

Make sure that the following steps are done before merging:

  • [ ] A DevOps team member has approved the PR.

  • [ ] Are you adding any new default values that need to be overridden when this change goes live? If so:

  • [ ] Update the appropriate internal repo (be sure to update for all our environments)

  • [] If you are updating a secure value rather than an internal one, file a DEVOPS ticket with details.

  • [X] Add an entry to the CHANGELOG.

  • [ ] Have you performed the proper testing specified on the [Ops Ansible Testing Checklist](https://openedx.atlassian.net/wiki/display/EdxOps/Ops+Ansible+Testing+Checklist)?

Done

Assignee

Cory Lee

Reporter

Open Source Pull Request Bot

Contributor Name

Daniel Clemente Laboreo

Repo

edx/configuration

Customer

Epic Link

None

OSCM Assignee

None

Platform Map Area (Levels 1 & 2)

None

Platform Map Area (Levels 3 & 4)

None

Blended Hour Utilization Percentage

None

edX Theme

None

edX Squad

None

Github Lines Added

None

Github Lines Deleted

None

Story Points

2

Priority

Unset