Fix 'Context: <blank>' fields in events.yaml and add build-time parsing check to ERROR if Context field not set correctly

[Agustin Carranza]

Brief Description
-----------------
Change all “Context: “ lines to “Context: none” … so they explicitly say they have no context and should not be published by automated docs.
And then change parseEventsYaml.py (a build time parsing checker) to generate an error if:

Context is not present in definition
Or
Context is present but has no value

Severity
--------
Minor: System/Feature is usable with minor issue

Steps to Reproduce
------------------
Add/modify an alarm with Context: <Empty>

Expected Behavior
------------------
Parser check rejects the change and informs Context field can not be empty.

Actual Behavior
----------------
Parser check ends successfully.

Reproducibility
---------------
100%

System Configuration
--------------------
N/A

Branch/Pull Time/Commit
-----------------------
master

Last Pass
---------
N/A

Timestamp/Logs
--------------
N/A

Test Activity
-------------
Developer testing

Workaround
----------
N/A

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/starlingx/fault/+/883860

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/starlingx/fault/+/883860
Committed: https://opendev.org/starlingx/fault/commit/6438565a4d9d50f63a0b46e207c5457595abc531
Submitter: "Zuul (22348)"
Branch: master

commit 6438565a4d9d50f63a0b46e207c5457595abc531
Author: Agustin Carranza <email address hidden>
Date: Mon May 22 13:40:34 2023 -0300

    Add parsing check when Context field is empty

    This change adds a parsing check to ERROR if Context field is Empty.
    Until now there had not been a requirement of non empty fields, so in
    case this is needed in the future for other key/values, a collection is
    created.

    Test plan
    PASS: * Add/modify an alarm/log in events.yaml file with Context field
            set to <Empty>.
          * Run the checkEventYaml script and check it fails.
    PASS: * Check that all the events in events.yaml file have the Context
            field set to a non empty value.
          * Run the checkEventYaml script and check it ends successfully.

    Closes-bug: 2020381

    Signed-off-by: Agustin Carranza <email address hidden>
    Change-Id: Ia267886dd49099525751165975fb5d291c0c6f82