Firebase Issues: grammatical errors fixed, improved formatting, added assets (#374)

* grammatical errors fixed, improved formating, added assets

* improved formating

* improved formatting, internal links updated, updated content

* Update docs/troubleshooting/firebase-issues/unable_to_validate_firestore_schema.md

Co-authored-by: Pooja Bhaumik <[email protected]>

* improved formatting, added new asset

* Update docs/troubleshooting/firebase-issues/client_access_to_firestore_expired.md

Co-authored-by: Pooja Bhaumik <[email protected]>

* correct asset updated, improved formatting

* updated content

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Co-authored-by: Pooja Bhaumik <[email protected]>

Author: mrdavidorok