Fix typos

[Marcofann]

This PR fixes several minor typos across multiple files to improve code readability and maintain consistency in comments and documentation. These changes are purely cosmetic and do not affect functionality.

Files and Changes:

• app/export.go
  • Corrected "a allowed address list" to "an allowed address list."
• app/genesis.go
  • Fixed "key'd by a identifier string" to "key'd by an identifier string."
• x/marketmaker/keeper/marketmaker.go
  • Corrected "by an pair id" to "by a pair id."
• x/marketmaker/keeper/proposal_handler.go
  • Fixed "is not a applied market maker" to "is not an applied market maker."
• x/marketmaker/types/keys.go
  • Corrected "by a address" to "by an address."