Add allowPaths to solr 9 configuration to fix backups

[hackartisan]

If you run a new backup (look at the crontab and copy the backup command, run it as deploy user) and then consult /tmp/solr_backup.log you will see request ids and can use those to check the status of the backup like so:

curl "http://localhost:8983/solr/admin/collections?action=REQUESTSTATUS&requestid=geniza-202501161456"

Currently we get the following status:

{
  "responseHeader":{
    "status":0,
    "QTime":4},
  "success":{
    "lib-solr-staging1.princeton.edu:8983_solr":{
      "responseHeader":{
        "status":0,
        "QTime":0}}},
  "geniza-2025011614562084550127003914":{
    "responseHeader":{
      "status":0,
      "QTime":0},
    "STATUS":"failed",
    "msg":"Failed to backup core=geniza_shard1_replica_n1 because org.apache.solr.common.SolrException: Path /mnt/solr_backup/solr9/staging/20250116/geniza-20250116.bk/geniza must be relative to SOLR_HOME, SOLR_DATA_HOME coreRootDirectory. Set system property 'solr.allowPaths' to add other allowed paths."},
  "failure":{
    "lib-solr-staging1.princeton.edu:8983_solr":{
      "responseHeader":{
        "status":0,
        "QTime":0},
      "STATUS":"failed",
      "msg":"Failed to backup core=geniza_shard1_replica_n1 because org.apache.solr.common.SolrException: Path /mnt/solr_backup/solr9/staging/20250116/geniza-20250116.bk/geniza must be relative to SOLR_HOME, SOLR_DATA_HOME coreRootDirectory. Set system property 'solr.allowPaths' to add other allowed paths."}},
  "Operation backup caused exception:":"java.nio.file.NoSuchFileException:java.nio.file.NoSuchFileException: /mnt/solr_backup/solr9/staging/20250116/geniza-20250116.bk/geniza/zk_backup_0",
  "exception":{
    "msg":"/mnt/solr_backup/solr9/staging/20250116/geniza-20250116.bk/geniza/zk_backup_0",
    "rspCode":-1},
  "status":{
    "state":"failed",
    "msg":"found [geniza-202501161456] in failed tasks"}}

It seems like there's something we could do in solr9 playbook to make this work.

See more at https://solr.apache.org/guide/solr/latest/upgrade-notes/major-changes-in-solr-9.html

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