[ncp] integrate SRP Server and Advertising Proxy for NCP

[Irving-cl]

This PR integrates the mDNS Publisher with NcpHost to make advertising proxy work under NCP mode.

The PR adds an expect test to verify the advertising proxy function under NCP mode. To do the test, avahi-browser is used. So it's added into the bootstrap of the CI for ncp_mode.

As an abstraction:

1. The PR adds NcpSpinel::SrpServerSetEnabled and NcpSpinel::SrpServerSetAutoEnableMode to control the SRP server on the NCP.
2. The PR adds the handling of SPINEL_PROP_DNSSD_HOST, SPINEL_PROP_DNSSD_SERVICE and SPINEL_PROP_DNSSD_KEY_RECORD to help NCP to publish the dnssd entries (by using the mDNSPublisher on the host).

[codecov]

Codecov Report

Attention: Patch coverage is 4.19580% with 137 lines in your changes missing coverage. Please review.

Project coverage is 45.88%. Comparing base (2b41187) to head (8cf6c5b).
Report is 891 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ncp/ncp_spinel.cpp	3.84%	124 Missing and 1 partial ⚠️
src/agent/application.cpp	0.00%	5 Missing ⚠️
src/ncp/ncp_host.cpp	16.66%	5 Missing ⚠️
src/ncp/ncp_spinel.hpp	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2624      +/-   ##
==========================================
- Coverage   55.77%   45.88%   -9.89%     
==========================================
  Files          87      106      +19     
  Lines        6890    12851    +5961     
  Branches        0      928     +928     
==========================================
+ Hits         3843     5897    +2054     
- Misses       3047     6632    +3585     
- Partials        0      322     +322     

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[abtink]

Looks good overll.
Couple of smaller suggestions. and one question/suggestion about key name.

[abtink]

We should be careful here, as the first label in a "service instance name" may itself contain a dot (.) character. So, if we construct a full name by appending the labels, it may be parsed incorrectly later.

[Irving-cl]

Added a check to only add the dot when the name doesn't contain one in the end.

[abtink]

The . can be in the middle and part of the instance name label itself (not a separator). The dot . is generally not used (or allowed) in DNS labels, but service instance labels allow this. For example, a service instance label can be "device.1234" as a single label (. being part of the label itself).

If we want to handle this, I can think of two options:

1. Keep the first label separate and pass it as a separate "string" to all APIs (mDNS-related APIs).
2. Add a new escaping mechanism so we can construct a full name as a single string, using an escape character to indicate when . is part of the label and not a separator.

I prefer option 1 (that's why we use this way to represent the names from the OT core).

I know this is rather tricky, so it may be fine to leave it for the future (accepting that the current code would not work with instance labels that include a .).

[Irving-cl]

SGTM! I added a comment in the code.

[zhanglongxia]

LGTM