chore(agent-job-notifications): Handle more error types

[balamurali27]

• fix(agent-job-notifications): Handle can't connect to mysql errs
• chore(subscription): Correct spelling
• fix(agent-job-notification): Handle corrupt backup restore attempts
• fix(agent-job-notification): Handle incompatible backup errs

fixes #2363

[codecov]

Codecov Report

Attention: Patch coverage is 37.93103% with 18 lines in your changes missing coverage. Please review.

Project coverage is 38.52%. Comparing base (1798667) to head (574b138).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
...press/doctype/agent_job/agent_job_notifications.py	37.50%	15 Missing ⚠️
press/press/doctype/site/site.py	0.00%	2 Missing ⚠️
press/press/doctype/agent_job/agent_job.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2401      +/-   ##
==========================================
- Coverage   38.54%   38.52%   -0.02%     
==========================================
  Files         377      377              
  Lines       29252    29286      +34     
==========================================
+ Hits        11274    11282       +8     
- Misses      17978    18004      +26     

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