Remove mongodb

[rem1niscence]

Remove all references of mongodb to only keep the postgres db as the only source of truth. This is done by

• Removing anywhere where mongo was used
• Removing fallback code from phd
• Modify all tests that needed to have some data from a db to use a HTTP mock to retrieve PHD results
• Add a small function to phd to return HTTP error objects in case the HTTP call fails

Although I tried my best to not modify any logic, a small change had to be done to the loadBlockchains function to return the expected Error response, besides that no other change was made to any logic

[height[bot]]

Link Height tasks by mentioning a task ID in the pull request title or commit messages, or description and comments with the keyword link (e.g. "Link T-123").

💡Tip: You can also use "Close T-X" to automatically close a task when the pull request is merged.