Switch the default trust threshold for new clients to 2/3

[romac]

Closes: #2876

Description

Note that the default trust threshold used for creating a client with create client when no trust threshold is specified on the command line is taken from the chain config's trust_threshold setting. We should therefore advise operators to update their configs with the new recommended value as otherwise the changes below won't have any effect outside of tests.

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PR author checklist:

• Added changelog entry, using unclog.
• Added tests: integration (for Hermes) or unit/mock tests (for modules).
• Linked to GitHub issue.
• Updated code comments and documentation (e.g., docs/).
• Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• Reviewed Files changed in the GitHub PR explorer.
• Manually tested (in case integration/unit/mock tests are absent).

[ancazamfir]

lgtm, thanks @romac !

[romac]

I wrote a little tool to fetch the latest 1000 blocks from the Cosmos Hub with a step of 1, 5, and 10 and compute the voting power overlap between all adjacent blocks. The results are here (there are multiple files each with a different step).

I did not see an overlap less than 2/3 so I would assume that the impact of this change in terms of client updates will be low if not null, at least on the Hub.

Will check with other chains with smaller validator sets.

[romac]

Ran some tests on Chihuahua, Evmos, Injective, and Secret and did not find a validator set change greater than 1/3 over any combination of the past 1000 blocks.

Let's merge this :)