Issue 53209: Allow externalModules folder to be dictated via application.properties file

[labkey-jeckels]

Rationale

We've long supported pointing to a custom external modules directory via a system property. We can also support using application.properties

Changes

• Look for context.externalModules in application.properties and use it to set the system property

[labkey-jeckels]

@labkey-jony installers queued for this feature branch: https://teamcity.labkey.org/buildConfiguration/LabKey_253Release_Premium_InstallersCustom/3534685

[labkey-jony]

Confirmed working.

Performed the following test:

• Spun up a trial instance and stopped Tomcat.
• Downloaded the labkey.org binaries mentioned above and installed the labkeyServer.jar to /labkey/labkey, replacing the original one for trial.
• Copied the evaluationContent.module file from /labkey/labkey/modules to /labkey/labkey/externalModules (I needed a module that didn't exist in the labkey.org binaries)
• Sanitized the trial instance for the test (removed startup properties files, dropped and recreated the database so it was clean, etc).
• Started Tomcat and went through the initial setup wizard
• Checked the module list on the Admin Console and confirmed that evaluationContent was there and mapped to /labkey/labkey/externalModules
• Stopped Tomcat and created a new optional.application.properties file
• Added the following line to optional.application.properties:

context.externalModules=/labkey/testdirectory/externalModules

• Created the folders to make /labkey/testdirectory/externalModules and moved the evaluationContent.module to that directory
• Started Tomcat and rechecked the modules page on the Admin Console
• Confirmed the module was still there and was mapping to the new location when looking at the module details.