docs: add changelog entries for v20 migration (#3334)

* add changelog for v20 migration

* migrations are also state-breaking

.changelog/unreleased/features/3308-ics-metadata.md

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+- Set the metadata for launched ICS consumer chains.
+ ([\#3308](https://github.com/cosmos/gaia/pull/3308))

.changelog/unreleased/features/3316-ics-props-migrate.md

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+- Migrate active ICS gov proposal to the new messages
+ introduced by the permissionless ICS feature.
+ ([\#3316](https://github.com/cosmos/gaia/pull/3316))

.changelog/unreleased/state-breaking/3263-max-provider-consensus.md

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+- Set the `MaxProviderConsensusValidators` parameter of the provider module to 180. 
+ This parameter will be used to govern the number of validators participating in consensus,
+ and takes over this role from the `MaxValidators` parameter of the staking module.
+ ([\#3263](https://github.com/cosmos/gaia/pull/3263))

.changelog/unreleased/state-breaking/3263-max-validators.md

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+- Set the `MaxValidators` parameter of the staking module to 200, which is the current number of 180 plus 20.
+ This is done as a result of introducing the inactive-validators feature of Interchain Security, 
+ which entails that the number of validators participating in consensus will be governed by the 
+ `MaxProviderConsensusValidators` parameter in the provider module.
+ ([\#3263](https://github.com/cosmos/gaia/pull/3263))

.changelog/unreleased/state-breaking/3308-ics-metadata.md

@@ -0,0 +1,2 @@
+- Set the metadata for launched ICS consumer chains.
+ ([\#3308](https://github.com/cosmos/gaia/pull/3308))

.changelog/unreleased/state-breaking/3316-ics-props-migrate.md

@@ -0,0 +1,3 @@
+- Migrate active ICS gov proposal to the new messages
+ introduced by the permissionless ICS feature.
+ ([\#3316](https://github.com/cosmos/gaia/pull/3316))