Change google.api.field_behavior -> aep.api.field_behavior

[rambleraptor]

Closes #109

This is a big PR. It changes all of the google.api.field_behavior logic to aep.api.field_behavior

[toumorokoshi]

Nice! Thanks for this mega-PR

[odsod]

should this say "set to FIELD_BEHAVIOR_REQUIRED on their string parent"?

semi-related note - why the added FIELD_BEHAVIOR_ prefix? asking since AEP-126 encourages dropping the prefix unless it's needed for disambiguation:

enum Format {
    // Default value. This value is unused.
    FORMAT_UNSPECIFIED = 0;

    // The printed format, in hardback.
    HARDBACK = 1;

    // The printed format, in paperback.
    PAPERBACK = 2;

    // An electronic book format.
    EBOOK = 3;

    // An audio recording.
    AUDIOBOOK = 4;
  }

Is is because there's a need to disambiguate REQUIRED within aep.api?

[rambleraptor]

I'll let @toumorokoshi answer that one. Docs changes have been made

[toumorokoshi]

@odsod good question! I primarily wanted to future proof enum values, as you mentioned.

This is also a default rule to lint against, e.g. in buf: https://buf.build/docs/lint/rules/#enum_value_prefix

[toumorokoshi]

I'm not holding on this opinion particularly strongly... maybe we can do a quick poll in the #aep slack to see what people think? link: https://cloud-native.slack.com/archives/C04TX46UCTV/p1760729260615679