The key words for conformance are misused. (UPPERCASES <-> lowercases)

[sunghee-hwang]

In the spec, the keywords are used somewhere in Notes and Convention.
And, there are still lower cases in the normative sections.

We should use "UPPERCASES" in the following normative sections:

• Section 2 Immersive Audio Model
• Section 3 Open Bitstream Unit (OBU) Syntax and Semantics
• Section 4 Profiles
• Section 5 Standalone IAMF Representation
• Section 6 ISO-BMFF IAMF Encapsulation
• Section 7 IAMF Processing

We should use "lowercases" in the other informative sections (Sections 1, 8, 9, and 10), notes, and examples.
Also, we don't need to use the keywords for conformance for the Convention section.

Here are examples of misusing in the spec.

• Section 2: Many "may" are used but "MAY" is used in a Note.
• Section 3: "MAY" is used in a Note.
• Section 6: "optional" is used.
• Section 8: "SHALL" is used.