Add mime-type guessing logic based on the filename, with default mime-types as fallbacks.

[osamahan999]

New mime-type logic which guesses the extension based on the file name using probeContentType in java.nio.file.Files. If we cannot guess the mimetype, we fallback on the item's specified mimetype. If that is empty, we then fallback on a default. The default for photos is 'image/jpg' and for videos 'video/mp4'.

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[seehamrun]

FYI it looks like the gradle test is failing on this file type:

GoogleMediaItemTest > getMimeType_photoModel_mimeTypeFromFilename FAILED
    org.opentest4j.AssertionFailedError: expected: <image/apng> but was: <image/vnd.mozilla.apng>
        at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
        at org.junit.jupiter.api.AssertionUtils.failNotEqual(AssertionUtils.java:62)
        at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
        at org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
        at org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1141)
        at org

[osamahan999]

Okay, I believe I found the issue here. According to the docs, probeContentType "uses the installed FileTypeDetector implementation to probe the given file to determine its content type."

Locally, my installed FileTypeDetector returns "image/apng" for 'file-name.apng', but it seems like in our pipeline we might have a different FileTypeDetector? I am not sure where this FileTypeDetector is coming from, maybe it depends on the OS running the pipeline? Or perhaps it is a Gradle specified detail? I can't seem to find more info on this, but I think the most important part of this is that it indicates that we must decide on a mimeType conversion convention to prescribe to.

[seehamrun]

Instead of focusing on testing the probeContentType implementation, i think its fine to focus on testing the fallback logic. so i think its fine to remove this file type from the test.

WDYT?

[osamahan999]

Makes sense to me! I do think we should make note of this though, since it feels like indeterministic code. On one machine the mimetype may be x, on another it may be y.