admin-server does not respect "config" URL parameter

[garrettjstevens]

Describe the bug

If you use the config URL param to open up a different config from the default ./config.json, it updates the default config, not the config specified in the URL param.

To Reproduce

jbrowse create jbrowse2
cd jbrowse2/
jbrowse admin-server

2. Open the URL that admin-server provides, but add a config location, e.g. http://localhost:9090/?adminKey=1ed63244e1&config=test_data_volvox_config.json
3. Edit the config (e.g. add/remove a track)
4. Instead of ./test_data/volvox/config.json getting updated, ./config.json gets overwritten with the new volvox config, losing any configuration that was already in that file. The config file might not be valid, either, as it may depend on relative file URLs that are not valid in that location.

Expected behavior

The config specified in the URL should be updated, not the default one

Version:

1.3.2