Add RUN_MIGRATIONS flag to the service configuration

[hectorgomezv]

Summary

This PR adds a flag to (de-)activate the database migrations execution at the service startup. The flag default value will be true unless it is explicitly set to false.

Changes

• Adds RUN_MIGRATIONS (true by default) to control the execution of database migrations at the application bootstrap.
• Adds a test suite for PostgresDatabaseMigrationHook.

[coveralls]

Pull Request Test Coverage Report for Build 9888310835

Details

• 1 of 5 (20.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 48.111%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/datasources/db/postgres-database.migration.hook.ts	1	5	20.0%

Totals
Change from base Build 9858819355:	-0.01%
Covered Lines:	4245
Relevant Lines:	7083

---

💛 - Coveralls

[hectorgomezv]

As discussed offline, we see this as a temporal security measure to provide a switch that allows the team to block the database migrations from running by setting an environment variable. For the longer term, we aim to build a more elaborate mechanism where specific migrations can be linked to feature flags, so these migrations would only apply to the database if the feature flag is active. (cc. @iamacook)