Extend /blog to enable more tag filtering & improve "subscribe"

[JeffLowe]

• [ ] Extend the blog's tag filter bar to handle the other tags, not just the original "events" "Updates" and "news"
• [ ] change case of the nft tag to be "NFT" and the ipfs tag to be "IPFS"
• [ ] consider better placement of the Subscribe button (perhaps out of the highlight area and near tag filter?). This is not directive, just something to examine and consider, as means of clarifying what user is subscribing to.
• [ ] Add explanation text to the subscribe page https://nft.storage/blog/subscribe/. Possibly “Enter your email to receive a notification when new blog content is posted.”.
• [ ] Success screen after user subscribes, update copy to "You are subscribed to the blog mailing list."

Raw feedback from Alan in #1498 Blog

• Entries are tagged but the tag filters list does not include those tags.
• Tag casing issues: “Nft” -> “NFT” and “Ipfs” -> “IPFS”. Blog Subscribe page
• Needs a better title “Subscribe” -> “Subscribe to the Blog”.
• Needs explanatory text: “Enter your email to receive a notification when new blog content is posted.”.