chore(deps): update etherpad/etherpad docker tag to v1.9.7

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
etherpad/etherpad	final	patch	1.9.5 -> 1.9.7

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Release Notes

ether/etherpad-lite (etherpad/etherpad)

v1.9.7

Compare Source

Notable enhancements and fixes

• Added Live Plugin Manager: Plugins are now installed into a separate folder on the host system. This folder is called plugin_packages.
  That way the plugins are separated from the normal etherpad installation.
• Make repairPad.js more verbose
• Fixed favicon not being loaded correctly

v1.9.6

Compare Source

Notable enhancements and fixes

• Prevent etherpad crash when update server is not reachable
• Use npm@6 in Docker build
• Fix setting the log level in settings.json

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