Update changelog for 0.50.0 release.

Fix mozilla-mobile#2344: 1535258: Fix dependency on Miniconda install…

… on build dir

Add glean timing distribution metric

Adds glean timing distribution metric, including it's storage engine, documentation, and unit tests.

0.47 release prep [ci skip]

0.46 release prep [ci skip]

Add changelog for 0.45.0

Update PR template with changelog link

Update changelog for 0.43.0 release.

Add changelog for 0.42.0

Closes mozilla-mobile#1944: Remove unneeded default arg of initWebView