Install mockgen

[wojtek-coreum]

Description

Reviewers checklist:

• Try to write more meaningful comments with clear actions to be taken.
• Nit-picking should be unblocking. Focus on core issues.

Authors checklist

• Provide a concise and meaningful description
• Review the code yourself first, before making the PR.
• Annotate your PR in places that require explanation.
• Think and try to split the PR to smaller PR if it is big.

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This change is 

[dzmitryhil]

Reviewed 1 of 1 files at r1.
Reviewable status: all files reviewed (commit messages unreviewed), all discussions resolved (waiting on @masihyeganeh, @miladz68, and @ysv)

[masihyeganeh]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @miladz68 and @ysv)

[miladz68]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ysv)