[DocDB] Ensure connection shutdown is only performed once

[karan-yb]

Jira Link: DB-7687

Description

As part of #18744 fix (https://phorge.dev.yugabyte.com/D27859), we added a change to ensure that we are only queuing the DestroyConnection once per connection. Figure out why we didn't run into this issue in prod, and simply the connection shutdown path by closing the connection inline.

I0818 10:07:31.725487 1868984320 connection.cc:134] 0x105a89d58 - Shutdown called with status Service unavailable (yb/rpc/reactor.cc:106): Shutdown connection (system error 58), existing Network error (yb/util/net/socket.cc:540): recvmsg error: Connection reset by peer (system error 54)
I0818 10:07:31.725772 1864396800 connection.cc:167] Connection (0x000000010758e7f8) server 127.0.0.1:59872 => 127.0.0.1:59864: Write failed: Network error (yb/util/net/socket.cc:447): sendmsg error: Broken pipe (system error 32)
I0818 10:07:31.727180 1868984320 connection.cc:167] Connection (0x0000000105a88fd8) client 127.0.0.1:59866 => 127.0.0.1:59864: Write failed: Network error (yb/util/net/socket.cc:447): sendmsg error: Broken pipe (system error 32)
I0818 10:07:31.727444 1868984320 connection.cc:134] 0x105a89d58 - Shutdown called with status Network error (yb/util/net/socket.cc:447): sendmsg error: Broken pipe (system error 32), existing Service unavailable (yb/rpc/reactor.cc:106): Shutdown connection (system error 58)
W0818 10:07:31.727458 1868984320 reactor.cc:758] Client_R000: Looking for Connection (0x0000000105a89d58) client 127.0.0.1:59871 => 127.0.0.1:59864

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