docs: updates bom and spanner version in readme (#415)

Author: yoshi-automation

README.md

@@ -17,7 +17,7 @@ If you are using Maven with [BOM][libraries-bom], add this to your pom.xml file
  <dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>libraries-bom</artifactId>
- <version>9.1.0</version>
+ <version>10.0.0</version>
  <type>pom</type>
  <scope>import</scope>
  </dependency>
@@ -38,7 +38,7 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-spanner</artifactId>
- <version>1.59.0</version>
+ <version>1.60.0</version>
 </dependency>
 
 ```
@@ -157,10 +157,9 @@ with `grpc.io/client/`.
 * `cloud.google.com/java/spanner/max_allowed_sessions`: This shows the maximum
  number of sessions allowed.
 
-* `cloud.google.com/java/spanner/num_sessions_in_pool`: This metric allows users to
- see number of sessions in the pool. You can breakdown this metric by
- num_in_use_sessions, num_sessions_being_prepared, num_read_sessions and
- num_write_prepared_sessions.
+* `cloud.google.com/java/spanner/in_use_sessions`: This metric allows users to
+ see instance-level and database-level data for the total number of sessions in
+ use (or checked out from the pool) at this very moment.
 
 * `cloud.google.com/java/spanner/num_acquired_sessions`: This metric allows
  users to see the total number of acquired sessions.

synth.metadata

@@ -4,7 +4,7 @@
  "git": {
  "name": ".",
  "remote": "https://github.com/googleapis/java-spanner.git",
- "sha": "77398f2771d5531b8f703c17df694dc77e42f35f"
+ "sha": "af9563098241b7c9030e83502ccc80e7038f982b"
  }
  },
  {