Backport of VAULT-9427: Add read support to sys/loggers endpoints into release/1.12.x

[hc-github-team-secure-vault-core]

Backport

This PR is auto-generated from #17979 to be assessed for backporting due to the inclusion of the label backport/1.12.x.

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The below text is copied from the body of the original PR.

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PR #16111 added support to modify server logging verbosity both globally and for individual loggers. It did not, however, add the ability to read the current state of the logger verbosity levels. This PR introduces read handlers for the sys/loggers and sys/loggers/:name endpoints.

Additional more low-level changes:

• Modified Core.SetLogLevelByName to account for the potential of Core.allLoggers including loggers that share the same name
• Modified existing sys/loggers handlers to use ParseLogLevel from the logging helper package to remove redundant code
• Added checks to ensure sys/loggers endpoints do not handle base logger (name == "")
• Added a TranslateLoggerLevel func to the logging helper package to determine the logging verbosity of an hclog.Logger

Example output on a dev server (vault server -dev):

# Set policy logger to trace level
❯ curl -XPUT -H "X-Vault-Token: $VAULT_TOKEN" -d '{"level":"trace"}' "$VAULT_ADDR/v1/sys/loggers/policy"

# Fetch verbosity level of all loggers
❯ curl -s -XGET -H "X-Vault-Token: $VAULT_TOKEN" "$VAULT_ADDR/v1/sys/loggers" | jq .data
{
  "activity": "info",
  "audit": "info",
  "auth.token.auth_token_cf840257": "info",
  "core": "info",
  "core.cluster-listener": "info",
  "core.cluster-listener.tcp": "info",
  "core.router": "info",
  "expiration": "info",
  "expiration.job-manager": "info",
  "grpclogfaker": "info",
  "identity": "info",
  "identity.storagepacker.entities": "info",
  "identity.storagepacker.groups": "info",
  "identity.storagepacker.local-aliases": "info",
  "mfa": "info",
  "policy": "trace",
  "quotas": "info",
  "rollback": "info",
  "seal.shamir": "info",
  "secrets.cubbyhole.cubbyhole_079cd5ab": "info",
  "secrets.identity.identity_7b1c0163": "info",
  "secrets.kv.kv_efb8658b": "info",
  "secrets.system.system_3ae59f37": "info",
  "storage.cache": "info",
  "storage.inmem": "info",
  "storage.sealunwrapper": "info",
  "system": "info",
  "token": "info"
}

# Get verbosity level of just the policy logger
❯ curl -s -XGET -H "X-Vault-Token: $VAULT_TOKEN" "$VAULT_ADDR/v1/sys/loggers/policy" | jq .data
{
  "policy": "trace"
}

# Revert verbosity level of just the policy logger to what is provided in config
❯ curl -s -XDELETE -H "X-Vault-Token: $VAULT_TOKEN" "$VAULT_ADDR/v1/sys/loggers/policy"

# Get verbosity level of just the policy logger
❯ curl -s -XGET -H "X-Vault-Token: $VAULT_TOKEN" "$VAULT_ADDR/v1/sys/loggers/policy" | jq .data
{
  "policy": "info"
}

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• 1440b0b

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