Make project size optional in project creation/edit flows

[blushi]

Describe the solution you'd like
Project size should be optional. We should update the current BasicInfoForm to account for that and add the "optional" label to the project size field.

https://www.figma.com/file/Sb9BavGvlCFPQFpjdDlwsL/Web-2.0-log-in-and-actions?type=design&node-id=341-33364&mode=design&t=pK72Nx0TdNFLoNKu-0

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[ryanchristo]

Marking this as blocked (needs further discussion, maybe confirm on design call) as there were some concerns about how projects would appear on pages where some had size and some did not and whether size should be required even if the project can only provide an estimate.