Add okcomputer health checks for system status

[elrayle]

Description

Add okcomputer gem and mount at healthz. Add checks for...

• solr
• redis
• mysql
• sidekiq

Related work

samvera/hyrax#4291 add a default health check endpoint at /healthz
samvera/hyrax#4292 - implement a solr health check

https://github.com/cul-it/usda-esmis-sufia/pull/1186 - Hyrax update 2.7.2

• https://github.com/cul-it/usda-esmis-sufia/pull/1186/commits/40aea8044a41995b30ccfbdb4d9603c1c5ed8c22 - initializer
• https://github.com/cul-it/usda-esmis-sufia/pull/1186/commits/529ee790e014ad304a2a4418a0760668cd14531b - lib code
• https://github.com/cul-it/usda-esmis-sufia/pull/1186/commits/15b61a5e6a06d6d04778b5fcae698a7f4a871836 - commented out routes
• https://github.com/cul-it/usda-esmis-sufia/pull/1186/commits/8f6d4ae3076748200b3e6b36194a777eb2a388d4 - locales

https://github.com/cul-it/usda-esmis-sufia/pull/1194 - Related publication -- uses ENV['REDIS_HOST'] for health check

[elrayle]

Fixed by PR #352