Expose OpenTelemetry APIs via MP Telemetry

[Emily-Jiang]

Fixes: #210

[Azquelt]

Also need to test this to check it actually functions as we want.

I think the two use cases are:

• Depending on it as a provided dependency to provide the OTel APIs at the correct level
• Adding it as a dependency to the org.eclipse.microprofile:microprofile artifact.

Edit: Tested that this does work:

        <dependency>
            <groupId>org.eclipse.microprofile.telemetry</groupId>
            <artifactId>microprofile-telemetry-api</artifactId>
            <version>2.0-SNAPSHOT</version>
            <type>pom</type>
            <scope>provided</scope>
        </dependency>

and if we update the umbrella API with a dependency on this API, this also works:

        <dependency>
            <groupId>org.eclipse.microprofile</groupId>
            <artifactId>microprofile</artifactId>
            <version>7.0-SNAPSHOT</version>
            <type>pom</type>
            <scope>provided</scope>
        </dependency>

I did have issues building the umbrella javadoc, but I'll raise a separate issue for that.