Enable tests for `AwsKeyManager` and remove `skip` on `keymanager-aws` `kover-maven-plugin` config

[ALRubinger]

In #322 we broke out the AwsKeyManager implementation and its test suite into its own module, web5-keymanager-aws.

This breaks the build in that new module, inheriting the coverage plugin's enforcement. Because all existing tests are marked as @Disabled, there is no coverage for the module.

To unlock the work in #322, we elected to move forward by disabling the kover-maven-plugin enforcement constraint, opting to enable the tests and re-add coverage enforcement later. That discussion is In PR #327.

This issue is the "later" cleanup task. :)

• Enable the tests, potentially as @mistermoe suggests using localstack.
• Remove the configuration that skips coverage enforcement in the web5-keymanager-aws pom.xml (ie. commit 1eb180c258d790822e77742b59d3f209dc7d6b3f:

        <plugin>
          <groupId>io.github.martinvisser</groupId>
          <artifactId>kover-maven-plugin</artifactId>
          <configuration>
            <!-- We temporarily disable coverage enforcement until we have tests working for this module -->
            <skip>true</skip>
          </configuration>
        </plugin>