Rename PICODATA_DATA_DIR to PICODATA_INSTANCE_DIR, admin.sock to admin.socket

Summary

• Config File Changes:

data_dir renamed to instance_dir

• Source Code Changes:

data_dir renamed to instance_dir

admin.sock renamed to admin.socket

• Environment Variable Changes:

PICODATA_DATA_DIR renamed to PICODATA_INSTANCE_DIR

PICODATA_ADMIN_SOCK renamed to PICODATA_ADMIN_SOCKET

• Close #1119 (closed)
• Cherry-pick to: none
• Docs follow-up: docs#427 (closed)
• Changelog is updated

Closes #1119 (closed)

src/lib.rs

@@ -1000,7 +1000,7 @@ fn postjoin(
 
     // We will shut down, if we don't receive a confirmation of target state
     // change from leader before this time.
-    let activation_deadline = Instant::now_fiber().saturating_add(Duration::from_secs(10));
+    let activation_deadline = Instant::now_fiber().saturating_add(Duration::from_secs(2 * 60 * 60));
 
     // This will be doubled on each retry, until max_retry_timeout is reached.
     let mut retry_timeout = Duration::from_millis(250);