Extend INDEXER_MEMORY_LIMIT env parsing

[sl1depengwyn]

Motivation

It's not obvious that value of INDEXER_MEMORY_LIMIT must be a single number (https://discord.com/channels/973915550965174292/992040622254997566/1072857553622540399)

Changelog

Added possibility to set INDEXER_MEMORY_LIMIT with suffixes like gb, g, mb, m independently of letter case. With no suffix interpreted as gb as it was.

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables. (Update related to #6929 docs#119)
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[vbaranov]

I suppose related doc page should be updated as well https://docs.blockscout.com/for-developers/indexing/how-do-i-update-memory-consumption-to-fix-indexer-memory-errors

[sl1depengwyn]

I suppose related doc page should be updated as well https://docs.blockscout.com/for-developers/indexing/how-do-i-update-memory-consumption-to-fix-indexer-memory-errors

Here it is: blockscout/docs#119
Thank you!