Add ConcurrencyLimitingService

[ikhoon]

ConcurrencyLimit will be useful on the server side to limit the current requests being handled.
However, we can't use ConcurrencyLimit on the server side because:

• It is located in the client package and;
  

  armeria/core/src/main/java/com/linecorp/armeria/client/limit/ConcurrencyLimit.java

  Line 17 in df2c0e9

  package com.linecorp.armeria.client.limit;

• ClientRequestContext is used as the argument of the acquire() method.
  

  armeria/core/src/main/java/com/linecorp/armeria/client/limit/ConcurrencyLimit.java

  Line 137 in df2c0e9

  CompletableFuture<SafeCloseable> acquire(ClientRequestContext ctx);

So we need to move ConcurrencyLimit to common package first and implement ConcurrencyLimitingService similar to ConcurrencyLimitingClient

package com.linecorp.armeria.common.limit;

public interface ConcurrencyLimit {
    CompletableFuture<SafeCloseable> acquire(RequestContext ctx);
}

Discord thread: https://discord.com/channels/1087271586832318494/1087272728177942629/1328988059827568752