Querying subs to query newly discovered publishers with publication caches

[Yadunund]

Fix #263

This PR:

• Renames Entity::keyexpr() to Entity::liveliness_keyexpr() to disambiguate between keyexpressions used for liveliness tokens and keyexpressions used for topic/service names.
• Adds topic_keyexpr string to TopicInfo stored within Entity. This way, entities constructed within GraphCache are aware of they topic keyexpressions.
• Adds an API to register callbacks to trigger when a Publisher with a PublicationCache is detected in the graph.
• Updates rmw_create_subscription to register a callback as described above that will call ze_querying_subscriber_get over the keyexpression. This requires the zenoh session ID as the "selector" to uniquely identify which PublicationCache to query.

[Yadunund]

This PR will likely remain in draft until we migrate to Zenoh 1.0.0. f4dc8ea set query_accept_replies to ZCU_REPLY_KEYEXPR_ANY but this option is passed at QueryingSubscriber creation and is used only for the initial query. It's not used for subsequent calls to ze_querying_subscriber_get which is what we need to fix the original problem.
The ability to pass this option to the ze_querying_subscriber_get() call that is triggered in the callback will only land in 1.0.0.

[Yadunund]

I've temporarily merged changes from eclipse-zenoh/zenoh-c#620 and I can confirm this PR now fixes the original issue. Once upstream eclipse-zenoh/zenoh-c is updated, we can re-update the vendored zenoh-c commit hash before merging. In the meanwhile @clalancette do you mind reviewing the changes?

[Yadunund]

The API in zenoh-c has been fixed and i've updated the commit hash accordingly. This PR is ready for review.

[Yadunund]

Hmm i've been unable to successfully run the nav2 demo with this PR. More specifically, the costmap does not show up in RViz and i'm unable to localize the robot. Digging into whether the problem is caused by the changes in the code here or perhaps a regression somewhere in zenoh-c between the old commit and the new one.

[Yadunund]

I've narrowed the problem to this line that this PR added

rmw_zenoh/rmw_zenoh_cpp/src/rmw_zenoh.cpp

Line 623 in 4188ea1

pub_cache_opts.queryable_prefix = z_loan(queryable_prefix);

If I comment out the line, running ros2 launch nav2_bringup tb3_simulation.launch.py headless:=False is able to successfully start up

Else I'm seeing

But the whole point of the bug fix is to include the queryable_prefix option to the publication cache. Perhaps some other options are not set correctly?

cc @JEnoch @imstevenpmwork @YuanYuYuan

[JEnoch]

@Yadunund this PR fixes this issue: #274

TL;DR: the QueryingSubscriber performs an initial query that must now be adapted following the addition of zid as a prefix in PublicationCache's queryable.
Detailed explanation in the PR.

[Yadunund]

@Yadunund this PR fixes this issue: #274

TL;DR: the QueryingSubscriber performs an initial query that must now be adapted following the addition of zid as a prefix in PublicationCache's queryable. Detailed explanation in the PR.

Thanks for the fix! I've merged it into this PR. This is now ready for another round of review.

[clalancette]

I've left one minor thing to improve. Once that is done, and @ahcorde 's comments are addressed, I think this will be good to go.

[clalancette]

Thanks for all of the changes here! Looks good to me.