Add support for file upload input to WPS.

[na9da]

What this PR does

Merge after #7668

Adds file upload input for WPS.

• Uploaded files are encoded to base64 and added to Execute request.
• ComplexData input not already handled by other input types are rendered as file input if it supports base64 encoding.
• Checks if the file is within the specified maximumMegabytes limit

Here is an example WPS input description that is rendered as file input:

 <Input minOccurs="1" maxOccurs="1">
                <ows:Identifier>upload</ows:Identifier>
                <ows:Title>Upload zip data File</ows:Title>
                <ows:Abstract></ows:Abstract>
                <ComplexData maximumMegabytes="1">
                    <Default>
                        <Format>
                            <MimeType>application/zip</MimeType>
                            <Encoding>base64</Encoding>
                        </Format>
                    </Default>
                    <Supported>
                        <Format>
                            <MimeType>application/zip</MimeType>
                            <Encoding>base64</Encoding>
                        </Format>
                    </Supported>
                </ComplexData>
            </Input>

Test me

• Open this CI link
• View the WPS item from catalog
• Test the file upload input field

Checklist

• There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• I've updated relevant documentation in doc/.
• I've updated CHANGES.md with what I changed.
• I've provided instructions in the PR description on how to test this PR.