Support multiple connections in the client mode.

[evshary]

Solve #2142

We added the EndPoints to accept a single EndPoint or EndPoint vector.

To test the multiple connections:

RUST_LOG=zenoh_transport::unicast::establishment=debug zenohd --cfg=transport/unicast/max_links:2
RUST_LOG=zenoh_transport::unicast::establishment=debug z_sub --cfg=transport/unicast/max_links:2 -m client -e tcp/127.0.0.1:7447?rel=1,tcp/127.0.0.1:7447?rel=0

Note that we use the , as the delimiter to split the multiple links.

[github-actions]

PR missing one of the required labels: {'dependencies', 'breaking-change', 'enhancement', 'api-sync', 'bug', 'internal', 'ci', 'new feature', 'documentation'}

[codecov]

Codecov Report

❌ Patch coverage is 73.09942% with 46 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.71%. Comparing base (f33fe8c) to head (d9095ba).
⚠️ Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
zenoh/src/net/runtime/orchestrator.rs	73.77%	16 Missing ⚠️
commons/zenoh-protocol/src/core/endpoint.rs	75.80%	15 Missing ⚠️
commons/zenoh-config/src/mode_dependent.rs	60.86%	9 Missing ⚠️
commons/zenoh-config/src/lib.rs	79.16%	5 Missing ⚠️
zenohd/src/main.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2320      +/-   ##
==========================================
- Coverage   72.98%   72.71%   -0.28%     
==========================================
  Files         387      387              
  Lines       62160    62089      -71     
==========================================
- Hits        45370    45145     -225     
- Misses      16790    16944     +154     

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[OlivierHecart]

This is a change in behavior.
Coma separated values were already accepted here and were the equivalent of passing multiple -e arguments.
Let's decide if:

• we assume this behavior change and add this in a minor release
• find another separator for this case

[evshary]

I personally prefer the first one, while the second one will make usage complicated.
However, it's still fine with me if we decide on the second one.

[OlivierHecart]

I also realize that we had plans to create locator groups for peers, where peer connect to a single endpoint of each group. We need to decide if this is still something we consider and how to articulate that with the multilink thing here.

[OlivierHecart]

Another point, I don't see any changes in DEFAULT_CONFIG.json5. It would be good to have this roughly documented there.

[evshary]

Another point, I don't see any changes in DEFAULT_CONFIG.json5. It would be good to have this roughly documented there.

I thought it would make the description too complicated, so I just skipped that.
I've added it to the config now.