Fix gas price in rpc endpoints

[thomas-nguy]

Closes: #XXX

Description

Currently returns gas_cap which is a wrong value for the gas_price

Fix also config parsing which was returning default previously

Todo

• Fix integration tests

---

For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

---

For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[orijbot]

Visit https://dashboard.github.orijtech.com?back=0&pr=568&remote=true&repo=thomas-nguy%2Fethermint to see benchmark details.