Enable CongestionControl::Block if QoS is reliable.

[evshary]

With DDS the only combination of QoS which makes a Publisher to block the publications in case of network congestion is with Reliability=RELIABLE and History=KEEP_ALL.
In order to closely mimic this behaviour rmw_zenoh is setting Z_CONGESTION_CONTROL_BLOCK only for this combinaison of QoS.

However, in case of a Publisher for a "latched topic", it will use such combination of QoS:
Reliability=RELIABLE, History=KEEP_LAST(1) and Durability=TRANSIENT_LOCAL.
This leads rmw_zenoh to set Z_CONGESTION_CONTROL_DROP for the Publisher. And in case of very congested network the single publication might be dropped. That's what happens in the case discussed here:
#38 (comment)

This PR solves this problem setting Z_CONGESTION_CONTROL_BLOCK for any Publisher with QoS Reliability=RELIABLE, whatever the other QoS are.

[JEnoch]

This looks good to me.
@clalancette could you please also review it and advise if we shall merge it to dev/1.0.0 branch now or if we shall wait the merge of dev/1.0.0 to rolling

[evshary]

@JEnoch Thank you for adding comments and a detailed description. I always admire the ability you make things clearer 😆
I will also test the PR with nav2 to verify it again.

[evshary]

I will also test the PR with nav2 to verify it again.

Okay, it works properly after the changes.