[RELEASE] Prepare release opentelemetry-cpp 1.20.0

[marcalff]

No release date yet.

Must have:

• [SDK] Implement spec: MetricFilter #3235
• Experimental network.interface.name slipped into stable semconv due to semconv bug #3251
• Prepare release v1.31.0 semantic-conventions#1970
• [SEMANTIC CONVENTIONS] Upgrade to version 1.31.0 #3294

Desirable:

• [METRICS SDK] Fix hash collision in MetricAttributes #3322
• [SDK] Add logger scope configurator #3282

[ThomsonTan]

It will be great to include the fix (in progress) for #3060 in this release.

[owent]

Including #3147 would be great, if possible.

[marcalff]

Including #3147 would be great, if possible.

Yes, this review is long overdue, sorry for the delay.
Getting the review done for 1.20 is really tight, but I will look at the recordable changes next week.

[lalitb]

I need to review for this release:

#3060
#3299