allow @files and externalModules dirs to persist on mounted storage

[labkey-willm]

Rationale

system maintenance files are being lost on container restart because they are being mounted as a Docker volume. Similarly, externalVolumes was unable to be used because it was also set as a Docker volume. This update moves them both under the /labkey/files directory, typically mounted to external storage, so they can persist over container restarts and upgrades.

Related Pull Requests

Changes

• remove @files as a Docker volume, so it comes in under the (usually external) /labkey/files mount
• remove system maintenance files > 90 days old (which will now persist under @files)
  • add PURGE_MTNC_LOGS_OLDER_THAN_DAYS env var, default to 90
• remove externalModules Dockfer volume, instead creating under (usually external) /labkey/files mount
  • add LABKEY_EXTERNAL_MODULES env var, default to /labkey/files/externalModules
• add context.externalModules to application.properties
• shift optional SLEEP to just before env var purge and java startup, for testing
• bump quickstart version to 25.8