Write upgrade messages, and incorporate step into release process

[indirectlylit]

Observed behavior

For release 0.14, we forgot to create strings advertising the 0.14 upgrade, which means we'll need to use upgradeMessageGeneric for most languages:

kolibri/kolibri/core/assets/src/views/UpdateNotification.vue

Lines 88 to 101 in 0beb63c

	// The strings below are not actually used in the appplication code.
	// They are included simply to get the strings translated for later use. We should do
	// this differently in the longer-term to ensure that we have broader language support.
	/* eslint-disable kolibri/vue-no-unused-translations */
	upgradeHeader: 'Upgrade available',
	upgradeHeaderImportant: 'Important upgrade available',
	upgradeMessageGeneric: 'A new version of Kolibri is available.',
	upgradeMessageImportant:
	'We have released an important update with fixes to this version of Kolibri.',
	upgradeMessage0130:
	'Kolibri version 0.13.0 is available! It contains major improvements to resource management, coach tools, and much more.',
	upgradeDownload: 'Download it here',
	upgradeLearnAndDownload: 'Learn more and download it here',
	/* eslint-enable kolibri/vue-no-unused-translations */

Additionally, the current release process checklist does not contain guidance on using the nutritionfacts_i18n.py script in order to distinguish custom messages from the generic one:

kolibri/build_tools/i18n/nutritionfacts_i18n.py

Lines 29 to 51 in 0beb63c

	@click.option(
	"--title",
	default="UpdateNotification.upgradeHeader",
	help="Title string ID",
	type=str,
	)
	@click.option(
	"--message",
	default="UpdateNotification.upgradeMessageGeneric",
	help="Message string ID",
	type=str,
	)
	@click.option(
	"--link-text",
	default="UpdateNotification.upgradeLearnAndDownload",
	help="Link text string ID",
	type=str,
	)
	def main(title, message, link_text):
	"""
	Generate JSON suitable for sending in nutrition facts notifications
	"""

Expected behavior

For 0.15:

• create an appropriate message prior to string freeze and put it in UpdateNotification.vue
• add this step to the "String chill and string freeze" section of the Release process developer docs so it's not missed in future releases
• update the release process checklist to give guidance on selecting custom messages when available

User-facing consequences

Existing users will not have enough context on the content of new major releases

Context

0.14.0