Add differential gene expression plot and table endpoints

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Pull Request Template

Description

Add the following differential gene expression (DGE) endpoints to transfer DGE heatmap PNG plots and JSON tables via HTTP GET method.

• /dge/top-gene-disease-gtex-diff-exp/json: Transfer a JSON table of one disease and top differentially expressed genes.
• /dge/top-gene-disease-gtex-diff-exp/plot: Transfer a PNG heatmap of one disease and top differentially expressed genes.
• /dge/gene-all-cancer-gtex-diff-exp/json: Transfer a DGE JSON table of one gene and all diseases.
• /dge/gene-all-cancer-gtex-diff-exp/plot: Transfer a DGE PNG heatmap of one gene and all diseases.

Issues resolved:

• Resolved #37
• Resolved #59

Notes for reviewers:

• The changes in this PR will be deployed to DEV site by 1/12/2022 or 1/13/2022. The database ETL process has been running. After ETL, the API HTTP server will be redeployed with the updated database.
• In the review, please only add comments or suggestions that are directly related code correctness or documentation readability.
• This PR is not broken into smaller PRs, because all changes in this PR are required to test whether the API works as expected or not. Most of the file changes are test results and plots.

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• [x] Integration test

Task link/Screenshot/Terminal returns:

$ ./tests/run_tests.sh 
API base URL: http://localhost:8082

✔ |  OK F W S | Context
✔ | 354       | tests/r_test_scripts/test_endpoint_http.R [612.5 s]                                                                                                                                            

══ Results ══════════════════════
Duration: 612.6 s

For more details about local testing environment, options, and resources, see README.md of this PR branch.

Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [NA] New and existing unit tests pass locally with my changes
• [NA] Any dependent changes have been merged and published in downstream modules
• [x] I have checked my code and corrected any misspellings
• [ ] I have emojis in my PR and commits 😉

cc @taylordm @chinwallaa

[logstar]

Hi @atlas4213 . Thank you for reviewing and approving this PR.

I will merge this PR soon, after coordinating with FNL team. The plan to merge this PR will also be discussed in the OpenPedCan-api PR review meeting this week.

cc @chinwallaa