Add plan limit for Terraform Module package file size

What does this MR do?

Adds a plan limit for Terraform Module package file size.

Terraform Module packages are being added as part of #321102 (closed) and this plan limit will need to exist for that feature.

Related to #321102 (closed)

Database

Migrations

Adds terraform_module_max_file_size column to the plan_limits table with a default value of 1073741824 (1GB).

Up

== 20210305145622 AddTerraformModuleMaxFileSizeToPlanLimits: migrating ========
-- add_column(:plan_limits, :terraform_module_max_file_size, :bigint, {:default=>1073741824, :null=>false})
   -> 0.0032s
== 20210305145622 AddTerraformModuleMaxFileSizeToPlanLimits: migrated (0.0033s)

Down

== 20210305145622 AddTerraformModuleMaxFileSizeToPlanLimits: reverting ========
-- remove_column(:plan_limits, :terraform_module_max_file_size, :bigint, {:default=>1073741824, :null=>false})
   -> 0.0032s
== 20210305145622 AddTerraformModuleMaxFileSizeToPlanLimits: reverted (0.0063s)

Does this MR meet the acceptance criteria?

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