Fix pgbouncer password override

[KonstantinPetkov96]

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• [ X ] I have filled in the "Changes" section below?
• [ X ] I have filled in the "How did you test this code" section below?
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  release branch

Changes

Fixes issues with special characters in database passwords when using pgbouncer. The fix should be backwards compatible as well. Introduces the option to specify 'passwordOverride' needed because of the issue described here : #163

How did you test this code?

Manually :
You can go to the chart folder and do :

1. helm template flagsmith --set pgbouncer.enabled=true --set databaseExternal.enabled=true --set databaseExternal.host=test --set databaseExternal.username=test --set databaseExternal.database=test --set databaseExternal.password=test --set=pgbouncer.passwordOverride='test%!asd' --output-dir ./output --debug - This should override the test password.
2. And you can also verify that the code works without the password override using : helm template flagsmith --set pgbouncer.enabled=true --set databaseExternal.enabled=true --set databaseExternal.host=test --set databaseExternal.username=test --set databaseExternal.database=test --set databaseExternal.password=test --output-dir ./output --debug
3. Look at each output in the output folder.

Closes #163