Add FundCommunityPool to supported Distribution Msgs

[fragwuerdig]

Hello. I politely ask to add FundCommunityPool msg to cosmwasm::std, because it is a "hot" feature for Terra Classic smart contract owners. This PR is a third follow-up in a series of follow-ups described by the following issues and PRs:

• Add Encodings For MsgFundCommunityPool from Distribution wasmd#1458
• Add MsgFundCommunityPool to the Distribution Msgs wasmvm#433
• [FEATURE] Add cosmwasm-std message for community pool  classic-terra/core#288
• Add MsgFundCommunityPool to the Distribution Msgs #1741

The changes include:

• add FundCommunityPool to the list of supported/serializable DistributionMsgs
• add serialization test
• add serialization test for the other DistributionMsg variants (for the sake of completeness)

Note that this would likely need to be merged after the above mentioned PRs have been accepted. Thank you for considering this. We appreciate your support.

[webmaster128]

@Mergifyio backport release/1.3

[mergify]

backport release/1.3

🟠 Waiting for conditions to match

• merged [:pushpin: backport requirement]

[webmaster128]

Thank you. LGTM. Just the feature gate and could you add an entry to the UNREASED section of CHANGELOG.md?

[fragwuerdig]

Ok. Done. Thank you.

[webmaster128]

Thank you! I'll get this on the 1.3 release right after #1593 is merged.

[webmaster128]

Merged in #1752. Thanks a lot!