Update cost-usage-details-mca.md

[imranmaszeri]

This PR updates the column name PricingModel to its correct version pricingModel for the MCA file schema, which is actually what is provided in the file when obtained through Exports (small letter p instead of capital P).

This distinction is important to address a use case where one would attempt to append a usage data in the EA format, which is:

azure-docs/articles/cost-management-billing/dataset-schema/cost-usage-details-ea.md

Line 55 in 97ad002

| 38 |PricingModel|Identifier that indicates how the meter is priced. (Values: `On Demand`, `Reservation`, `Spot`, and `SavingsPlan`)|

The EA format uses PricingModel and appending this to the MCA format to perform a continuous cost analysis across months before and after change to MCA will not be successful.

I do not know if previous versions of the MCA schema did actually use PricingModel as I cannot prove this through Exports, so I am only updating the most recent version of the schema

[prmerger-automator]

@imranmaszeri : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[prmerger-automator]

@imranmaszeri : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit c40e504:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/cost-management-billing/dataset-schema/cost-usage-details-mca.md	✅Succeeded

For more details, please refer to the build report.

[ttorble]

@vikramdesai01

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team