Add Sentry for exception monitoring

Why these changes are being introduced:

We want to prepare for TIMDEX-UI as a potential production
application.

Relevant ticket(s):

https://mitlibraries.atlassian.net/browse/TIMX-81

How this addresses that need:

This adds sentry-ruby and sentry-rails, including the required
initializer.

Side effects of this change:

* Configures Sentry environment. We haven't done this yet in our
Rails apps, but it seems like it will be especially useful for
TIMDEX and TIMDEX-UI, for which we have a lot of different
environments.
* Added SENTRY_ENV and SENTRY_DSN to Heroku config vars.

Author: jazairi

Gemfile

@@ -11,6 +11,8 @@ gem 'jbuilder'
 gem 'mitlibraries-theme', '~> 0.7.0'
 gem 'puma', '~> 5.0'
 gem 'rails', '~> 7.0.2', '>= 7.0.2.3'
+gem 'sentry-rails'
+gem 'sentry-ruby'
 gem 'sprockets-rails'
 gem 'stimulus-rails'
 gem 'turbo-rails'

Gemfile.lock

@@ -247,6 +247,11 @@ GEM
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2, < 3.0)
       websocket (~> 1.0)
+    sentry-rails (5.4.1)
+      railties (>= 5.0)
+      sentry-ruby (~> 5.4.1)
+    sentry-ruby (5.4.1)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
     simplecov (0.21.2)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
@@ -326,6 +331,8 @@ DEPENDENCIES
   rubocop
   rubocop-rails
   selenium-webdriver
+  sentry-rails
+  sentry-ruby
   simplecov
   simplecov-lcov
   sprockets-rails

README.md

@@ -53,6 +53,8 @@ change as part of the work.
 `basic_search#index`.
 - `GLOBAL_ALERT`: The main functionality for this comes from our theme gem, but when set the value will be rendered as
   safe html above the main header of the site.
+- `SENTRY_DSN`: Client key for Sentry exception logging.
+- `SENTRY_ENV`: Sentry environment for the application. Defaults to 'unknown' if unset.
 - `TIMDEX_INDEX`: Name of the index, or alias, to provide to the GraphQL endpoint. Defaults to `nil` which will let TIMDEX determine the best index to use. Wildcard values can be set, for example `rdi*` would search any indexes that begin with `rdi` in the underlying OpenSearch instance behind TIMDEX.
 - `TIMDEX_SOURCES`: Comma-separated list of sources to display in the advanced-search source selection element. This
   overrides the default which is set in ApplicationHelper.

config/initializers/sentry.rb

@@ -0,0 +1,6 @@
+Sentry.init do |config|
+  return unless ENV.has_key?('SENTRY_DSN')
+  config.dsn = ENV.fetch('SENTRY_DSN')
+  config.breadcrumbs_logger = [:active_support_logger, :http_logger]
+  config.environment = ENV.fetch('SENTRY_ENV', 'unknown')
+end