CP-48570: Load recommendations from config file when Xapi starts

[BengangY]

1. Add a field 'recommendations' in pool.
2. The recommendations are read from files /etc/xapi.pool-recommendations.d/* and exposed to clients. They are read-only and only for clients, hence they don't impact the behavior of Xapi directly but only indirectly as they inform a client's behavior.
3. When Xapi starts, it will read each file and update the recommendations into the database.
4. If we need to add recommendations to other type objects e.g. host, VM, etc in the future, just add a similar xapi.*-recommendations.d directory and define the path in xapi_globs.

[psafont]

The recommendations are put in the config file '/etc/xapi.conf.d/recommendations.conf'. When Xapi starts, it will read this file and update the recommendations into each object.

This description doesn't seem accurate. To configure pool_recommendations, any .conf file in xapi.conf.d will suffice, with a line containing pool_recommendations, for example, pool_recommendations = boosters=2 carrots=tasty

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Additional details and impacted files

@@                    Coverage Diff                     @@
##           feature/vm-anti-affinity   #5637     +/-   ##
==========================================================
- Coverage                      51.3%   45.5%   -5.9%     
==========================================================
  Files                            13      13             
  Lines                          1925    1624    -301     
==========================================================
- Hits                            988     739    -249     
+ Misses                          937     885     -52     

see 11 files with indirect coverage changes

Flag	Coverage Δ
python2.7	45.5% <ø> (?)
python3.11	?

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[lindig]

In my earlier comments I misunderstood the purpose of the recommendations. My current understanding is:

• they are read from a file and exposed to clients
• they are read-only; hence the problem of storing large values that I mentioned before does not exist
• the recommendations are for clients and don't impact the behaviour of xapi directly but only indirectly as they inform a client's behaviour

[BengangY]

Codecov Report

All modified and coverable lines are covered by tests ✅

Additional details and impacted files

Why does codecov/project/scripts decrease to 36.6%? This PR didn't change scripts or *.py. And I didn't find the commit with ID d6d9454.

[minglumlu]

In my earlier comments I misunderstood the purpose of the recommendations. My current understanding is:

• they are read from a file and exposed to clients
• they are read-only; hence the problem of storing large values that I mentioned before does not exist
• the recommendations are for clients and don't impact the behaviour of xapi directly but only indirectly as they inform a client's behaviour

I think the above can be added into commit message.