feat: api server flags to start command

[akhilkumarpilli]

Description

This PR will add api server flags to start command so we can enable api directly from command instead of modifying app.toml.

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[julienrbrt]

LGTM 👍🏾

I wonder, however, why don't we use the values from config.DefaultConfig() directly instead of copying them. This way it stays for sure coherent between the default flag and the default app.toml.

[anilcse]

Thanks @akhilkumarpilli , lgtm
@alexanderbez comments need to be addressed.

[likhita-809]

lgtm