feat(abciclient)!: limit concurrent gRPC connections

[lklimek]

Issue being fixed or feature implemented

What was done?

1. Implemented concurrency control for grpc - right now, it is possible to limit number of concurrent grpc connections per method name (like 'query' or 'checktx')
2. Added new config section [abci] and moved relevant settings there
3. Defined [abci] grpc-concurrency option - see toml.go for more details

How Has This Been Tested?

Implemented unit test.

Breaking Changes

Changes in config file:

• created new [abci] section
• abci moved to [abci] section and renamed to transport
• proxy-app moved to [abci] section and renamed to address

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[shumkov]

👍

[github-actions]

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