dev/cloud-native/issues#18: Soften messages for read-only extensionsDir

[eileenmcnaughton]

Overview

Improve messaging when someone has a different policy for managing extensionsDir. Most of the messaging update has already been done. There is only one message ("Read-Only Extensions"). It still encourages web-writable policy, but it lowers the severity and presents it a choice ("if you want X, do Y").

replaces #12623

Before

The message that is displayed is a warning when the directory is "Read-Only" which implies something is wrong.

After

The message that is displayed is a notice when the directory is "Read-Only". notice says it's merely out of the ordinary

Comments

This a continuation of this PR #11895.

dev/cloud-native#18

Giving merge-on-pass as a reviewer's commit

[civibot]

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[seamuslee001]

Merging as per the tag