Improve error handling when fetching blog feeds

[sserrata]

Description

Adds additional error handling to the getBlogs and getHashicorpBlogs to prevent build failures when transient errors occur.

Changes include:

• Running curl commands in --silent mode to suppress output
• Adding a fall back that writes empty "[]" to json files
• Combining both commands into getAllFeeds to simplify usage

Other changes:

• Add optional chaining the Medium component to allow for handling empty json array
• Add getAllFeeds to start script to help ensure they are always generated/present
• Update gitignore to ignore feed json files

Motivation and Context

Helps overcome an otherwise annoying developer/contributor experience where running yarn start resulted in an error when blogs/feeds hadn't been fetched. Also, hopefully solves for situations where the curl commands may fail to fetch one or more feeds.

How Has This Been Tested?

Tested locally by using /etc/hosts so simulate a connectivity issue.

[github-actions]

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